Hi There is nothing wrong with some simple foreskin stretches that cannot be pulled back fully. If your foreskin of an uncircumcised penis becomes trapped behind the glans penis and can pull back to its normal in flaccid position please check with specialist for paraphimosis, in which it is a medical emergency as surgery is must. In your case, If you have a naturally tight foreskin relax the skin with lukewarm water which may loosen and relax the skin before stretching and be gentle. Any pain in that case is an indication of an underlined damage. Please consult ayurveda doctor/ specialist for the same.