When I first attended college I did so because I received a scholarship that covered my first year of tuition. I did not know how many resources were available to find scholarships or federal aid. I would have told myself that there are many resources available to me and I need to do a lot of research to find those scholarships and speak with the staff at the college to find out more about work study and other ways to cover tuition. I would have also told myself that I am an adult now and no one is judging me. If they are, it doesn't matter because they will not be in my life forever. I don't need to be scared of giving a speech or answering questions in class because we are all there to learn. The only way I am going to learn is to be an adult and ask questions, ask for help from staff or students, and to not be afraid to learn. College is more self-study too, so I do have to take initiative and schedule study time and down time. Overall, I need to relax, ask questions, and prioritize my time.
I would tell myself not to waste so much time on the stupid stuff; don't worry about what everyone thinks and make more friends. Life outside of high school is completely different and problems you're having now are nothing compared to what you could be facing. Enjoy life more for what it is and remember that whatever you decide with you future will be better then doing nothing. Don't take just one semester off because it will never be just one semester. Focus on doing something with your life to make yourself happy not to please everyone else in your life.
I would tell myself to strive harder in high school, and to take extra classes instead of trying to take the easy way to get through high school. The transition from high school to college is much harder when you have taken a year and haven't had to apply yourself. I would also tell myself to try to work harder on scholarship applications because they can make all the difference in the world for tution costs.