If I had the opportunity to sit down with my younger self I would tell her to not be afraid. Life is going to put you on your ass more times than you'd hope for, but do not be frightened. The most important lessons life will ever teach you are when you are at your lowest. Growth is formed just like a diamond, under a f**k ton of pressure young lady, but, the pressure is what you need.
"Healing is the end of conflict with yourself", acquire the skill to heal as a way to cope with your debilitating anxiety and you can start really fulfilling your dreams. TRUST ME. You must work to love yourself inside and out, so you can start helping others. I know its hard, but it will be the single best move you have made in your life.
Savor the small things. Cooking a perfect chicken breast, finding a new favorite shade of nail polish, a good hair day. Sounds silly to a 15-year-old version of me, but, it's one of the secrets of true happiness. Life will never be perfect, so you might as well start enjoying as much as you can. You never know when your short trip on earth may end.
Fitness will be your anchor and, true passion in life. It will allow you the outlet you need to be at peace with yourself. It will be there during the good times and the horrible ones, but, it will always be there. You will one day become a provincially qualified bikini competitor (the dream of nationals is still a work in progress), It will teach you the self-discipline you need excel and so much more.
Oh, yeah, and one last thing. Don't take yourself so damn seriously Hun.