Credit: Kamil Krzaczynski/

Amber Portwood has been doing a lot of soul searching since being placed behind bars on December 19.

In a letter to her brother obtained by TMZ, the 21-year-old Teen Mom star said she misses spending time with her family, including her 3-year-old daughter, Leah (with ex-boyfriend Gary Shirley).

"I don't think I'll ever take this sh-t for granted," a discouraged Portwood wrote. "I'm really scared I'm going to prison. I don't know what I'll do. All I think about is Leah and how she needs a role model. If I can get out, I can really show her what a good mother is."

"I don't want people thinking I'm this crazy bitch," the MTV star added. "I am a good person and I pray that I can change my life!"

Portwood -- who also apologized for her poor penmanship, explaining that "the pens they give us bend so we can't stab anyone" -- argued that she's not really an "endangerment to society."

"This sh-t is getting out of hand," she complained. "I wouldn't hurt anyone!"

Portwood is scheduled to appear in court on January 27. If convicted, the Teen Mom star faces up to two years in prison.