Mrrzy, how about writing down the reason(s) why you want to sing at the open mic, and bringing it with you to the venue as a reminder? I find that I chicken out in two circumstances: when I'm worried about not being "good enough" and when I think it's the "wrong" kind of audience. I sing successfully, or at least happily, when I remember that the song I have chosen is a great song that I want to share with others; the song becomes more important than the singer, freeing me from much of the worry about being good enough and allowing me to concentrate on telling the story of the song. But sometimes I really need to remind myself of that, so maybe writing your motivations down (whatever they are) would help. Then again, maybe you just need to wait until it feels right, or maybe you would like a different venue better. Are you reasonably comfortable with the scene at this particular open mic?