So... I've been working with my OSAP this evening with half a brain and then submitted it.

I went through all details several times before I submitted it.

An hour after I have submitted it, I decided to take a quick look at it again.

Turns out, I chose an option without looking at the other choices so now, my answer appears to be half-right.

My question is, if I go to the Student Aid office at Mac tomorrow, will they be able to make the correction for me?
I'm planning to hand in the required documentation as well (signed pages).

I made a similar mistake. For me, they said to write the correction manually and attach it with the signature page you mail. But it'd probably be easier if you go in person. Or you could call tomorrow and ask what the correct procedure is, if you don't feel like coming in.