Hello, one of mine came out a bit wide but only by 32nd which is awful close to 1mm, once the plate support gusset goes on it helps too.
If you felt it needed i suppose a small shim could be inserted to save it.
I wouldn’t rely on screws-and-glue to stop the slight movement for ever. I think it’d develop ‘play’ over time. Sawhorses tend to take a fair weight, sometimes used as a makeshift working platform to stand on.
I’d make the gap larger and insert a substantial dovetailed shim to the top-beam-recess.
Or cut the beam again from new. Legs 2,3,4 went OK, so you’ve mastered the technique, and you’ll be happier with it.