alright, I'm going to say it... I think they had enough room to move out of that position... But my boy stay getting lucky.
Room, yes. But do they trust themselves not to make a sound?
It's so blatantly contrived it has to be intentional. Here's my conspiracy theory: the mangaka
tried to get the permission to actually depict the sexual side of their budding relationship, but was effectively told it would be a step too far, and so decided to end the manga rather than have them be inauthentically chaste. She's just putting in whatever she can get away with at this point, clichéd contrivance be damned.
A less conspiratory take: the author simply wanted to demonstrate the extent of Komura's (and Mie's) character development. Remember when he wasn't able to sleep in his own room from sheer excitement for an entire weekend because Mie's
glasses were there, sitting on a shelf? When he would apologize in his mind to Mie's father in mortification at the slightest provocation? Well, look at what happens in this chapter and how well they both are taking it now, haven't they come a long way?