Question: When Peter meets up with Gwen after Uncle Ben leaves the school, what does he mean when he says he got "community service"? Does he mean Uncle Ben's request to pick up Aunt May or replying to Gwen's answer of getting expelled?
Answer: He's telling Gwen that he's been grounded.
How? Peter doesn't tell Gwen that he's "grounded" nor did Uncle Ben tell Peter he's "grounded".
Community Service was probably a way of saying that Peter was grounded.
Answer: He was replying to Gwen's question about being expelled. He didn't get expelled and the school wasn't going to make him pay for the broken backboard, but instead gave him community service, as a way of paying for the backboard and punishment.
Bishop73