Marines Open Contract?

Alright so this is probably one of my last questions for a while but here we go. I dep'd in to the USMC just last sunday. I was planning on shipping in December but things have kind of got to hell around here and I want to leave soon. I talked with my recruiter and he said I can leave in August but only open contract. He said with my ASVAB score (92) and line scores (all were 125+), I could easily get the job I want which is Artillery. My question is, has anyone gone Open and gotten the contract they want? How does it work? Any info will be greatly appreciated.