A remedial math teacher is forced to wonder if he wasted his potential as a screenwriter when his ex-highschool sweetheart, now a hollywood actress visits their hometown.

I agree with the previous comments. Wondering about a wasted potential can't give you a movie, not even one scene. What is the goal of the main character? What kind of opposition to this goal?
"When a big movie star come back to his old town for a a shooting, her ex high-school sweetheart have one week to prove her he can write the best role for her if he wants to win her love."

I agree with the comments above. There doesn't seem to be much of a "story" apparent in this logline. I would suggest that you go back and re-work your plot to include a definitive action and a definitive goal. Then, maybe his renewed interest in his former high school sweetheart could be further explored as the B-Story to the main plot.

Yeah, I agree. Get rid of 'is forced to wonder' and replace it with something active that the reader can visualise. Also, try to state the genre. Is this a comedy or a drama?