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.

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.

Add knobs to the drawers and doors and make it LOOK normal. Opening drawers from the center and straight out will help some. If the cabinet is particle board, it will fall apart in a couple of years anyway, and you can replace it with something better at that time.

Get rid of the square corner sink that is difficult to clean and not logical, and replace the ugly black faucets with chrome or gold.

RNmomof2 zone 5 is correct, inset or partial overlay door and drawers would solve the problem. I think the least costly fix would be to keep the tops you have and replace the cabinetry with 48" partial overlay or in-set style doors and drawers.

Also this is not completely the contractors fault. This is a result of lack of communication and forethought by both parties.

Your main problem will be, with all the discussion, is unless you get it done correctly, it will always bother you.