my swimming perf are bad help

hi guys , so am 15 am a boy and i practice swimming and every week i go on a meet the actual problem is my perf sucks and in the first day i started training i was bad all my friends are just better why cause when i was young i was very skinny now my physique is acceptable but my friends physique are superior and am week i have lack of strength and mobility but the endurance am super cardio and lately i started a good diet 3000cal per day and it's very difficult and i always training hard but my coach is kinda stupid and he don't really care about the strength training and mobility pls help me and if you need some photos of my physique am here