First offense class A Misdemeanor (state of Missouri)?

I was booked for attempted blackmail (although it was a prank, my ex, toward whom this prank was directed, did not seem to think so, and so she called the police on me). Anyway, I went willingly down to the police station, gave a willing statement, cooperated fully with the officers, and said I was plead guilty to being really stupid and putting this girl through the ordeal. I have never been arrested, never been involved in ANY crime whatsoever up until this point. My court date is in a month. I'm just wondering if I will get jail time. My arresting officer told me I did not need a lawyer. So I don't know...