High school. Military. College. Military?

I'm gonna be a senior next year and I'm not doing very well on my grades. I'm on the Texas minimum graduation plan and I'm joining The Navy when I get out. But in order to be an officer (which I want) you need to go to a four year college or better (which I can't). I also really want to be in law enforcement in the Navy as well as when i get out of the Navy. But not police. I wanna take down really bad people or do my very best to help. But once again i need four year college.

Basically I need to know if I preform better in the military than i did in high school, will a four year college (like the University of Houston) consider accepting me. Other wise I may end up having to take a 2 year college so i can go to a 4 year college.
(please don't say i should of done better in high school. That would be very unhelpful cause i already know that)