I leave. Our gym literally has 10 feet of space where we all enter and leve, you can touch the beam from the front door

. I usually arrive to see the last 15 mins of gym, but that is always conditioning.
11.45 - 12.45 on Saturday at our gym is always a riot. 25 girls are ending their course at 12:30 and 25 are beginning theirs at 12:00, 50 pairs of snow covered winter boots, assorted parents and sibings just turn the whole scene into a comedy. Wet socks and lost water bottles lying everywhere.
When my kids did one or two hours a week I stayed to watch, we also had a bigger gym then, but now I know they are fine. so I leave.
I would do what works for you and your child, and fits in with the gyms policies, oh yes....and space!!!
I do envy those of you with actual viewing rooms with space to work in at gym, that way at least you could achieve something else whilst being there.