Caught trespassing at Walmart, given court summons, what will likely happen?

Basically, I signed a no trespass "notice" or whatever they're called over a year ago when Walmart thought I was shoplifting (I was not, I got a lawyer and the charge was dropped). I had been going in to the SAME STORE ever since the first charges were dropped for OVER A YEAR, but today apparently someone recognized me and pulled me back to the office, called a cop, and I was given a court summons for trespassing. My lawyer explicitly told me "don't worry about that" when I told him about the trespass notice during the first 'charge'. Did Walmart have the right to do this, since they are not technically owned by the courts, or was this just extremely ridiculous and bitter employees trying to get me in court again because I 'escaped justice' when the lawyer proved I had NOT shoplifted at all, simply stuck a book under my purse in my cart to keep it flat and out of the mass of groceries in my full cart.

If I just plead guilty (some have said this is usually the best thing to do), what would happen to me? If I decide to plead not guilty, would it be best to get the same lawyer I used for the first case to handle this one for me or just go on my own and explain that I had no idea I was trespassing since my lawyer explicitly told me that it wasn't a problem and not to worry about it. I don't plan on mentioning my other forays into the same store, since apparently no one had recognized me or cared, unless bringing up how I'd been going to the store for a year without anyone saying/doing anything would help me.

I don't want to go to jail, and the police officer and Walmart woman heavily implied that I WOULD NOT go to jail over this, but I still have doubts and I am worried. I live in Jefferson County, Missouri, USA, and only have one previous misdemeanor, not at all related to trespassing. Also, the court denied me a court appointed attorney during the first charge and I had to find one and pay him $750, which I could do at the time, but now I am laid off. How would I go about getting a lawyer if I need one? Is there any way the court could be forced into giving me an attorney since I CANNOT afford to pay my previous lawyer? The court date is Sept 11 this year, so over a month away. Please help if you can!