When i was your age short while ago i felt the exact same. Good practice is to make sure your penis (mainly the head and around the foreskin) is wet to help is glid rather than rub during masturbation, spit works fine, just make sure you havent eaten anything that could cause irritation not long before like spicy stuff. In the shower is also good for constant moisture or underwater in the bath. Or using a small amount of lube and just pull it back more and more, bit by bit at a time and build your way up to pulling it back all the way and once there push it back and keep repeating so it stays stretched and not just pulled back with no repetative train