Grand theft charge.

I'm in a tough situation. I'm a recovering heroin addict who addmitts she stole from a neighbor. I took a birthday card off his door that contained $50. He has me on camera and is pressing grand theft charge saying there was over $500 in the envelope. I don't exactly have a great name in the system. I'm wondering what will happen. I live in NJ and 500$ is jail time. Im not trying to justify my actions because I do believe in Justice for all. But I'm being charged for something that is a lie. Should I get a lawyer or just go up and face the judge and plead the truth. Cause that's what I'm going to do. I want the truth out. I was a drug addict who wasn't on her physicatric meds and was dope sick. I refused to sell my body so I stole from a neighbor. Which may I add ... I gave $50 back in a blank card that said I'm sorry. I'm sure he found it on his porch