RNB - You're only 15 and have not finished growing yet.
That means you will have bits and pieces that are not yet the right shape, that stick out a bit and so on.
By all means do the abdominal exercises and keep the food healthy. Avoid too much carbohydrate and gassy drinks as that will make you bloat anyway.
Go and have a chat to a doctor or a counsellor, quietly, and see about working on your self esteem. You've nothing to worry about.
Man, if I was 15 again, with what I know now!!
Live it!