This was my experience, too. It’s a fun build, but it does have a bow. I added 3/8” thick bumpons on the corners and two 1/8” thick bumpons on the middle edges. That really helped with the sag. I ordered the real bricks on the Lego website and I’m going to try to rebuild it with those.

I put in Aquakings and clear Drop polystyrene keycaps and I think it looks and sounds pretty good.