1. As others here have advised, be patient. Keep training and take advantage of opportunities to race against guys on the team. Show a positive attitude and some consistency, beat some "B" team dudes, and then see what happens.
2. Keep in mind that simply making the team could be a mixed blessing. The quantity and quality of workouts (and the pressure on you as a walk-on to keep up) *might* be more than is ideal for you at this point. Personally, in retrospect, I would have done better as a runner to have gone to a less competitive school because I was always killing myself to keep up in workouts. So I'd suggest that your goal not simply be to get on the team, but to be in shape enough to get on the team *and* handle the workload that will follow.
3. It's probable that in order to put you on the team the coach would have to cut someone else. If he/she had done so, then this thread might well be entitled, "I Had One Bad Race and My Coach Cut Me!" with everyone bemoaning the coach's lack of loyalty and ultra-quick trigger finger. Would you really want to run for a coach that would make that decision based on a single race? Thus see point #1.