What do your plans indicate for the pool size vs what was done? Have you spoken with your builder about it?

Talk to your contractor. You may be just going through the shock of seeing something more solid then just a hole in the ground. Do not forget that the colour of the pool and the coping and the landscaping etc will all lighten it up.

For me, sometimes in the thick of building things can see too big or too small but later when everything is finished you say to yourself. Wow it worked. So before rushing to change it, lets see what your contractor says and what your plans show. Do you have the plans of what you are doing? Or are you permitted to share them? Your contractor is the best person to talk to about these concerns. Fingers crossed it all works out.

I have no idea we did not have any actual plans or pics of the yard. I agree often one thing seen in an empty lot has just made the whole thing look different . If you actually want to know then we need detailed plan of the lot and the plans for the pool and the decking . There are usually rules about pools and clearances and fencing all of which still needes to be done so talk to your contractor and your builder . IN the mean time pics please posted here in jpeg in comments DO NOT start snother post.

Photos help us help you.

Without them, and having just gone through a build, I can say that many things feel GINORMOUS (or WAY too small) and weird and out of place and whatever, when they're still under construction. The final product will look quite different from what it looks now in a partially-finished state.

Whether a pool is too big or too small for a back yard will be very subjective. Some people want as big a pool as they can cram in, while others will want to keep some yard space.

Hopefully one of the pool pros will read this and give you more detailed information, but pools can be remodeled. You are probably talking about having to do demolition, tie in new rebar, fix/reroute plumbing and re-pouring.

Do you have the budget to pay for basically redoing most of the pool work again?

If it fits in your yard, it's not too big, ime. growing up with a big pool. The play space for kids will be appreciated. Just swimming laps or playing blind lag larger is better. A pool makes more functional use of yard space than anything else I can think of, ime. Black tile and coping will make it appear smaller.

Some reply from the OP would be nice . We take the time to answer I think the same from the OP is a must.

In my experience, usually people prioritize overall size, shape, depth/slope, sun ledge, etc based on pool use. E.g. laps, sports, etc.

I'm with the other folks in that often a project looks all wrong while it's being done. We have had a lot of threads about it.

Out of curiousity, if it was supposed to be dug and left to settle till spring, why did they go ahead with the pour now instead of waiting?

Thanks everyone. I’ll try to get a picture to post for reference, since I’m sure that would be helpful. I’m sure there’s definitely some element of “shock” in simply seeing the giant hole in the ground and not being able to visualize the finished product (I’ve struggled with that with the whole building project).
My primary question initially was around the feasibility of shortening the length and pouring a new wall on one end. Perhaps even asking that question displays my incredible ignorance as to the process.
I haven’t spoken to my builder about it yet because, frankly, I don’t want him to think I’m a lunatic. In embarrassed that I didn’t really process ahead of time the size/scope of the pool. We kind of just went ahead with what was recommended by the pool company (based on our family size, etc,). So- to many of your points - perhaps I just need to sit tight and trust the experts.

Thank you for your brutal honesty. Wouldn't the pool company know to leave room for other activities such as outdoor dining or ping pong, stuff like that. Or did you just say we want a pool?

Your pool builder should have given you detailed drawings with dimensions of the pool, patio and distances to the house. It was part of our contract and needed for permits.

I made sure we had plenty of space for people to hang out around the 2 sides closest to the house, because I have been to, and seen, pools that are way too close to the house, with little room for circulation.

@nyg127 Thank you for your honesty. I truly believe it might just be shock at the scope and a little miscommunication with the pool designer. Before you post anything... Please talk with your GC or builder. You would not want to put them on the spot with their business reputation on the line with photos etc.. I am sure your post was more in reaction and hoping someone else had a similar experience. I am certain it will all work out. Do show photos if the GC and pool people are okay with it.

A photo of the half finished pool won't affect the reputation of an unknown GC or pool builder, but would allow others here to look at the size and give an opinion on the scale of it compared to the yard space available. Right now we are all guessing.

A homeowner should never need to ask permission to post photos of projects being done on their property. That seems like an odd suggestion to me.

Thank you again to everyone for your thoughts and honest feedback. My original post/question was more around the logistics and feasibility of actually shortening the length of a pool by pouring one new wall, but instead you all have helped me see that it’s actually probably going to be just fine. We did get drawings and of course knew the dimensions ahead of time, I just didn’t actually “process” the scope of it all when I couldn’t see it in space.
Since nothing can be done for the time being, I’m going to sit with it and see how my feelings about it change (or not) through the winter. My partner feels better about it than I do, so to a degree it’s all about perspective.