I'm able to retract my foreskin easily when non-erect or 50% erect, 70%-somehow and painless, but can't when 100% erect. is this curable with stretching?

? Due to frenulum: Frenulum is small web between urinary opening ; underside of foreskin. This will not respond to stretching ; may need to be divided. Very minor office procedure under local anesthesia. However, application of prescription strength steroid cream, such as 0.1% Betamethasone to tight area, twice daily for a few weeks, whilst trying to stretch would likely help.