If the foreskin is not coming back that is known as Phimosis. It requires a minor surgery to correct. During the visit size problem can be addressed.

Penis size doesn't affect your sexual performance. Most of the times person have misconceptions about their penis size while in reality it fall under the average size for that particular population. Regarding foreskin one of the most common reason is inflammation due to infection. Gently clean the glans and remove any smegma collection. Many a times proper hygiene is sufficient to relieve the problem but if it continues then do consult a doctor.