For starters, you need to begin to assemble a list of prospective colleges. Then, begin to shape your credentials using this summer to help you do that. There are a lot of options, many lasting only a couple of weeks. That gives you plenty of time for soccer. You might also want to work a little harder in school next year.
Grades do count.
In my mind, the best letter of recommendation is one that can speak specifically about your ability to perform at a certain school. So and so will do well is going to be a powerful statement. Other letters, from respected people, also carry weight. Personally, I would never sign a letter of recommendation for someone that I hadn t written myself. Maybe you know people who don t care.