Hi! I'm a senior, but I'm actually in the same boat as you. I began running as a sophomore, without any prior athletic experience. However, I quickly improved, finishing 2nd on my team and in the top 25 overall at the state meet this season. I began by contacting coaches at academically strong D3 schools (think: NYU, Williams, Tufts, etc.) this past summer. Some of them were very interested and made me offers. This winter, I contacted the coaches at the D1 schools I applied to, stressing my high grades and SAT score as well as my potential for improvement. I'd suggest that you do the same - I heard back from three of the six coaches I emailed! They were all very supportive, with some even setting up meetings with me or sending me their recruiting standards, telling me they believed I had the potential to meet them this year. Don't give up, and don't listen to the haters on this thread. Although many people on this site seem to be genuine fans, many of them are middle-aged men who have peaked in their running careers, or who are armchair experts about running. Best of luck to you!
(My pr's are sub-19 for 3 mile, sub-20 for 5k, sub-5:30 for 1600, and 12:11 for 3200.).