From the sheepish prompt you've given, I'll bet the email you sent the coach was even weaker.
This isn't rocket science. Be honest and upfront. State your purpose and be business like...
"My name is X (insert name), and I am an admitted student matriculating in the fall at X-University (insert name). I was an all-league distance runner in highschool. I broke 10min for two miles (insert PR) and was all-state in XC (insert place# at states). I want to continue running in college and I think i can improve greatly. I have begun my summer training and I would like to speak with you about try-outs for the team at X-university. My home phone number is (xxx)-xxx-xxxx (insert phone number). I look forward to hearing from you. Sincerely, X (insert your name)"
Then follow up with a very brief follow-up phone message that says: "Hi My name is (X) and I wrote you an email about fall tryouts, my number is (xxx)-xxx-xxxx please feel free to contact me at any time as I have voice mail- I'm really looking forward to hearing from you and running in the fall." (click)
PS- Coaches respect honesty and assertiveness. You've already been accepted to the college, so the hard part is over. And if this isn't a National Championship team, I can't think of many coaches who don't want people that don't cost them scholarships or have to be recruited and are academically eligible by regular matriculating standards...
Stop being a sissy- and ask her out already!
As P-Diddy would say "act as if you've been here before!"