@Incis0r gives very good advice, and there's nothing wrong with what he's said. I'm going to offer an alternative to his advice, which again, is solid advice and not wrong by any means.
-hang out with your friends because your time with them is dwindling
-do well enough in school and on your SATs to get into your state's flagship university (save money w/ in-state tuition, lots of opportunities, good experience living there)
-look into combined BS/DMD programs as mentioned (UConn has one), and don't stress at all about not being accepted to them
-start looking into volunteering that interests you, and that you enjoy, not because you're obligated to do so
In college
-try to get a feel for a rough skeleton of a schedule for your time in undergrad, in terms of what classes to take during which semester, when to take the DAT, when to get all your shadowing hours in. Be flexible because it will probably change, but at least take the time to pencil it all in
-make time to prioritize your grades. If you don't procrastinate or have a drinking problem, you should be able to handle it
-try to take one night off per week from doing any school work, and use that time to enjoy college. The rest of your time should be devoted to school/ECs/work etc
-don't stress out about anything. Just keep your grades up and do the best to stick to your timeline.
Worrying about dental school at 17 is not just uneccesary; it's dentrimental. Be a kid for the last remaining time during which you can. Nobody here will ever say on their death bed "I wish I spent less time with my family and friends and more time planning out my life to the T" This isn't to say being proactive and motivated is a bad thing. However, there is a happy medium which I'm sure you can find.
When you have specific questions about the process that can't be found using Google, there will always be plenty of people on here, including myself, willing to help you out. Keep browsing SDN periodically throughout college for advice.