it's so lucky that the main character read ahead in the manga chapter and noticed that she wouldn't attack him so that he could decide to focus on saving the princess. That was a smart move from him.
I think the original meaning might have been slightly lost in translation. It makes sense to me if he meant something along the lines of "I should've been the more prepared one" as in he should have steeled his resolve or used caution upon noticing them first. This translation is a bit patchy in...
surely it would be more important to have the person who defeated your examiners on your side instead of him going to a rival guild and then being an asset to that guild with the reputation of defeating your best members.