USMC Infantry/03xx question?

Hello im currently 17 years old and i'm a junior in high school. I'm planning on joining the United States Marines Corps as soon as i graduate from high school, But the only MOS i'm willing to do is Infantry. I really want the MOS 311 but if i don't get it I'll do anything in infantry. However i heard that Infantry gets full very fast. How hard would it be to get into the MOS field of 311? and how hard would it be to get ANY job in Infantry? Thanks