Hi KeplerJunior,
Nice to see you interested in joining the 'fold' so to speak. As both an astronomer and astrophysicist, and with a background in environmental engineering, I find that chemistry is both interesting and useful; however, the chemistry used for both astronomy and astrophysics isn't really that difficult. We are more interested in physical chemistry (size of atoms/molecules and the relation between these and properties such as electronegativity, the forces between atoms, etc, plus concepts such as the emission and absorption of various wavelengths by molecular species in sundry extreme environments - high pressure, temperature, velocity, etc); nothing too difficult. You can pick most of this up later on. I don't mean to sound flippant but what people say about chemistry is usually fairly apt -- that chemistry is just the physics of the outer electrons. :-)
Mathematics at a higher level would be useful, but then again it's always good to spread yourself out and give yourself as broad a knowledge base as possible, especially with the way employment prospects are looking at the moment. I, myself, took high level maths in high school (but not the highest, as that's taught during first year uni). This allowed me to branch out into Chemistry and Biology as well before getting to university (and then carried this on into the first year or two at tertiary level). To be a well-informed scientist requires a broad knowledge base in as many different disciplines as possible. Then again, I find that most of the top people in the field are highly specialised and focused. They are very successful - but you'd be surprised how many of these 'guys' (and 'girls') couldn't change a car tyre, fix their own computer or carry on a light-hearted conversation.
Broaden your skills and knowledge base, work on your lateral thinking skills, and don't lose sight of the beauty of the world around you, and you'll be fine.