NTRP is not an objective measure of skill. If you're a junior you aren't playing NTRP tournaments/leagues so you are not going to have the match results to validate a self-rated NTRP. That said, NTRP guidelines have minimums for self-ratings if you've played any college ball. Put it this way: you don't get to play college tennis because you think you're a 5.0, but you'll be initially rated a 5.0 for league play because you played college tennis.
What you need to ask yourself is if you honestly think you deserve to play college tennis. Wanting it isn't enough. What have you done to distinguish yourself as a player from the rest of the guys?
As for those teams who will take anyone to fill out a roster spot, it's probably not worth playing on such horrible teams. You'd probably have more fun playing club tennis/USTA Tennis on Campus at a big state school.