Anyone wanna bet MC is going to get zero recognition for what he's done, and the girl will instead think the other guy saved her?
Seems likely.
Well, he might be able to show his transformation to her later and she'll know he was the one who saved her from the centipede monsters before he messed up and left her passed out while getting dragged by monsters.
I'd say the main issue right now, beyond dealing with these monsters is that at some point he's going to get back to the fourth floor, see that she's gone and start searching for her, except he's not going to find her.
It might be that the others get in trouble again, and he finds them and help them, so he does end up getting recognition. To be clear, since the alternative is that he gets expelled since he's still at 0, he has to be recognised by someone. People are definitely going to ask themselves questions about the monsters he managed to kill, since the guys they sent all got killed, and since its an artificial dungeon, there may be surveillance cameras around that caught him. In fact when his friends were diving, they could be seen on a big screen.
So maybe he'll manage to remain stealthy about his intervention until the end, but someone is going to examine the evidence afterwards and find out his secret powers (it might take some time, while he basically drops out and his friends keep training and getting stronger). If not, I'm not really sure how the plot can progress.