So, you've got two MCs who won't talk honestly with each other, but you've realized too late you need to lock them in with each other or the story can't progress, but you've also set the story in university, so you can't just lock them in the gym storage room like in every single other manga in existence.
Thus: University automatically locks its doors at 11 pm, fire safety concerns be damned, and there's no night security staff you can give a quick phone call to get you out or nothing.
Well... I guess there probably is a sensible policy in place for this case and they only have to spend like an hour or so waiting. That's still long enough to be uncomfortable, so they'll have to talk, right?
Or bone, I suppose. There's always that option, too.