Improve my self-esteem

Well, I thought i was doing pretty good on this goal.. Maybe Slowly but progressing…
and then today the people from my school called and said that since i marked i was less active “and other things i indicated” (a.ka. Im fat) I couldnt go on the orientation trip I wanted to go on. Ive spent 6 months trying to convinvce my self that even though im fat, im still worthwhile, i can still do things, and they crushed all my self esteem in a 5 minute phone call..
Oh yes, hello, weve never meant you but weve given up on you because your fat, and so were sure you cant do this. good bye..

I dont know, the trip was supposed to be the big start of the new chapter of my life..and now im just getting written off yet again?

i think, that, through my other goals, ive realized thaty my very warped self esteem/self image in the main cause of many of my problems. I dont think i really need to improve my “self esteem” per say, as in learn to love everything about me, but i need to fix my self image some, so i can honestly look at myself and say I’m okay, and not being lying to myself.

And honestly, I have no idea how to do this.