Does the fit look weird being so tight?

Yes it does.

if there's any ideas for a fix?

Only ones that involve a saw and paint.

A 27" sink base and 18" drawer stack, or 24 and 21, and a filler on each side would have fit better.

Post a picture or two with a door and drawer open so we see how it's built.

Can the center doors open past 90°? We have to be careful with ours lest the door frame crack. Filler between door and drawer would have been better for us.

PPF nailied it above. At thuis point the GC needs to step up and tearout drywall, and making the openings lightly larger, no shoe horn method, definitely looks off and I imagine over time you will hate the functionality. Or replace it with the proper size and fillers. Stand up for yourself NOW.

How did this come to be? Did you want a 'built in ' look or really need the largest vanity that would squeeze into the hole? As stated above smaller vanity with trim would get you a built in look, look better and make using the drawers easier. Sorry but you need to start over with a different vanity.

This came to be because the alcove measures just under 48 inches. We were told to get a 48" vanity with the plan to shave the drywall and the vanity sides to fit.

From what I understand, the next vanity size down is 36" which would look silly with that much filler. Ya think?

Or we were given the option to have a custom build but an expensive cost. Mind you, we have two vanities like this as this is a Jack & Jill remodel.

We're meeting with the contractor tomorrow. Fingers crossed it goes well.

Maybe pulling it out and replacing 1/2" drywall with 1/4" might do the trick but who advised this choice you say you were told to do it so by whom? Wayfair has many 42" vanities which IMO better and the only other choice custom IMO

The contractor told us what size to order for this. We chose the vanities at a local distributor.

Custom would have given you more storage with bigger drawer boxes.

These have a lot of frame space. that takes away from potential storage space.

Your contractor should have told you to select a 42" vanity. I would put the issue re: the vanities back on your contractor. Your contractor is the expert and directed you to select 48" vanities. He/she was wrong.

You should not have to settle for vanities that don't function well. Based upon the comments you've received from pros, the vanities are the wrong size. Your contractor can either let you select a smaller vanity + use fillers to fit the space OR pull the vanities and replace the current drywall with 1/4" drywall (only if that will provide enough room).

Do not let your contractor try to push you around - you are not being picky.

The full overlay cabinets are the real issue. Would have had some breathing room if the drawers/doors weren't full overlay and there was frame showing.