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If you can't tell your mom or anyone else that can help you financially, there really is nothing to recommend for you unless you can afford to pay for your own surgery. Gyne surgery is usually not covered by health insurance because it's not a "health" issue; it's considered a voluntary cosmetic procedure because it has nothing to do with disease or being sick.
All I can tell you is that these boards are full of guys that dreaded and put off telling their parents about their gyne, but were pleasantly surprised when they finally did tell them. I assume your mother loves you. And because of that love, she would do anything to help you in your time of need. If she knew how much you were hurting and embarrassed, she will want to help you, and she will if she can. Embarrassment is common with gynecomastia, even though it is a VERY common condition. But it's not your fault. The reason you have it is not due to anything YOU did. You're just one of the millions of guys that have it. If your mom's not educated about gyne, educate her. Find some good articles on it and give them to her to read. Have her look at some posts here that you think are especially good and capture what you want her to know. Give them to her, let her read them, and then tell her that your gyne is adversely affecting the quality of your life. Be honest with her about how it makes you feel. She will be able to relate to being embarrassed in front other people, etc. Everyone has experienced that and knows what a miserable feeling it is. Your mother will not want you to go through that.
You deserve to live life normally, and based on what you wrote, you can't really do that right now. Therefore, surgery is not simply a luxury for you, it is a NECESSITY! You're going off to college and it's SUPPOSED to be the very best time of your life. Don't allow it to be less than that. There will be countless times when you will need to be able to take your shirt off in the coming years. You need to do everything you can to put yourself on the right path to leading a normal life, and you can only do that with surgery. Established gynecomastia can't be treated with pills, exercise, weight loss, etc. Only surgery can "cure" gyne that has been present for 2 or 3 years, or longer.
Ballpark figure.....typical gyne surgery costs $5,000 to $8,000. I encourage you to tell your mom, otherwise, you're setting yourself up for a life of misery when it doesn't have to be that way. Don't pass up a lifetime of happiness and feeling perfectly normal when all you need is a surgical procedure that takes only a few hours to complete. Just do what needs to be done and get on the road to happiness and living life the way it was meant to be lived.