The biggest differenc you will see between the level you are currenlty playing at, whether that be high school or junior college, and the next level you go to (junior college, D III, DII or D I) are these three things: bigger, stronger and faster.

Players at the next level are going to bigger, stronger and faster than you are and that you have faced before.  They are going to have greater abilities to stop you, get by you, jump over you, and be more effective simply becuase they are either bigger, stronger or faster or are a combination of more than one.

So you have a choice, you will either need time to catch up once you have proven you have the technical skill to play at that level, or you can arrive to that next level just as athletic as they are, or close behind.

Keep in mind, college coaches want to win and some may need to win to keep their jobs.  They will put those players in the game who are the most likely to help them win games.  Don't give them an opportunity to tell you you are lacking in any of the mental, technical or physical areas of your sport.