I took the NAPT in June, and its not anything to be scared of. I hadn't taken a math class in a couple of years, and I was given little time to study (My recruiters told me the day of the test that I had to take it, which was somewhat frustrating.), but I had enough time to look over some basic principles of chemistry and physics, and that helped me quite a bit.
The test I took was multiple choice, which I've always felt tests your reasoning skills more than your actual knowledge. The math wasn't hard, but there is some you may not know how to do. Answering wrong doesn't count against your score and if you're able to count out a couple of answers you have a good chance of getting it right.
I got a 68 out of 80, which isn't amazing, but it's quite a bit above what I needed. My score was largely a reflection of my reasoning skills rather than my knowledge. Like I said earlier, it would be a good idea to look into the basic principles of chemistry and physics if you don't already know them. Also, try to brush up on some basic algebraic principles. There is some higher math, but knowing the basics will get you through.
Good luck!