Your letter is only a reflection of how you feel. It’s a “mess” because you feel like a “mess”. You are so discouraged about the possibility of making changes that you are giving up on yourself — even more than your friends have. Generally, teenagers don’t hang around with someone just because they feel “bad” for them. It’s more likely they like you but are as discouraged as you are about how to help you.
I agree with you. Some professional help would probably be helpful. But only if you are honest with your feelings. We therapists only have what people tell us to go on. If you do decide to see someone, please take this letter and response with you and share it. Doing so will help the therapist quickly get to your issues and be more helpful.
It might also be a good idea for you to share your letter with your mother as a way to help her understand how seriously discouraged you really are.
If seeing a professional isn’t possible, please look into joining a support group here at PsychCentral. Go to the “Find Help” tab on the home page. Then click on the “forums and support groups”. You will probably find a group of people who can offer you support and practical advice.
I wish you well.