https://www.khanacademy.org/
Scroll down to math (or just pick a diffrent subject). I assume you're somewhere at algebra, geometry and precalc.

Also, while things in highschool go SLOW, if you're interested you can go much faster and catch up faster than you'd think. While it's hard to teach yourself at this pace, keeping the pace high forces you to practise the basics more.

As an autodidact, no matter how good you are at maths, you'll get stuck and have questions at times. If you honestly can't figure out what something means, google it, ask someone, wikipedia, wolframalpha (mathworld), ..., but one way or another, FIND OUT. Don't give up until you understand both the answer to your question and where your confusion came from. Giving up on small parts just leaves holes in your understanding, which will bite you in the ass sooner or later.