Where is the logic in this argument?

I got accepted to my first choice school, both my parents agree I will go there no matter what, already got lots of school gear. I go to accept my admissions offer and my dad flips a shit, saying I have to wait to hear from FAFSA so I know my financial options, but they can take a few weeks to a few months to release decisions. If i'm going here anyway, why can't I accept my offer now?? I'm fine with taking out loans, money won't be an issue (Engineering Major, always in demand, and this school had one of the highest employment rates in the country). I wanna accept now so I can get a spot in the residence halls,which can only house 1/3 of the total students. Where is the logic in waiting potential months to go somewhere I will go to in the end?? BTW mom is all for me accepting the offer now...