Good for you!! Going back to school is a smart move that you're doing for YOU. What he thinks about it means less than nothing.
There are often jobs available to students through the job placement office that aren't offered to other people -- internships, work study, and job jobs. You may find a whole new world of opportunity, and maybe find something that really makes you happy.
If the test is an assessment -- assessment tests are just that -- for assessing where to put you. They help the school recommend where to place you in the progression of classes...somewhere on the ruler between College Basic Math and Genius Calculus. I did terribly at my math test too -- and I'm a computer geek!!
So don't worry. The tests are to help them help you. If you're worried, the library often has great books that will help. Ask the reference librarian to help you find them.
We're so proud of you, Starr.