Your best bet is to look up sample problems online and see how you do.  You can also find sample tests if you get a book (from the library or you buy one), I think (at least they have them for the SATs).  So that might give you an idea of what you want.

Ultimately, it's better safe than sorry... you have to pay, and it can be a large deciding factor on whether or not a school will accept you, so it's your choice.  Studying won't make you do worse, it can only make you do better...