To control premature ejaculation, stop and start technique is recommended but isn't doing that affects penis muscles or any structure responsible for sperm/semen release? what happens to the semen which was about to release but forcefully stopped???

The semen wait until it is time to be released. They really don't have much of a choice.

No it will not affect any part of the penis. The semen eventually comes out. Stop-start method requires patience and practice and an understanding and co-operative partner. Keep trying- good luck

You may be to anxious for sex and get excited too quick. Learn to relax, have a glass of wine or listen to soothing music before sex. Take it slow and talk to your partner and tell a funny joke.