I'm not in the CAF yet, so take this with a grain of salt, but as a teacher it sounds like whether you join the military or not, you have some things about yourself you'd like to work on.
You can take this whole experience as a way of focussing yourself on these things and pushing past your insecurities, but if you go in with a negative self-image and let the experience beat you down, you're setting yourself up to fail. Even just the way you write about yourself, it feels like you're talking down about yourself a lot. Other people pick up on this stuff very easily, and it trains other people on how to treat you. If you were just in high school (you sound young), all those other kids judged you back in grade 9, and that first impression probably stuck with them all the way through school.
Nobody in the army met and judged you in grade 9- they're meeting you now, so all that old baggage is irrelevant, start fresh! Go into this with the mentality that you will get tougher and stronger and that you will meet some great people who will like you too (can't be everybody all the time, but it will be somebody), and that you will be a good team member-- if you can manage that shift in mentality, I think you'll be taken aback at how much better people treat you from the outset, and how much easier socializing with them becomes after that. If you don't respect yourself first, why would you expect anyone else to do so for you? Start by taking pride in the fact that you're choosing to do a Hard Thing that a lot of people don't have the guts to even try. When it's kicking your ass, remember that you chose this ass-kicking and that alone makes you tougher than most.
