I have taken it years ago. I was also worried about math - I was terrible in math throughout school, I mean truly TERRIBLE.
I placed higher than I thought I would, but not high enough for my major (one class short of college level math), I took 5 quarters of math classes one at a time, I am a science major so I needed to finish Calculus. Taking math as an adult was the best thing ever! For the first time I actually understood it and had fun in math class.
Anyhow, the test is not 'difficult'. It reacts to your answers, if you answer a lot of questions right, you get bumped to the next level. If you start answering a lot of questions wrong the test will automatically end and that is the highest level you reach.
The test is not timed (at least not at our college) and you can take as much time as you want. In my college you could even take a break and return to the test the next day if you needed to.
If you did fine in HS you will probably do fine on the test - and if you don't, take a class at your level and retest - sometimes if you have been out of it for a while it comes back to you after using that skill again. It's like riding your bike, if you haven't done it for years you will be shakey at first but you soon regain your confidence.
Good luck!