If the retraction was only one time, there was probably no permanent damage done. The human body has a wonderful ability to repair itself and most likely this is what has happened. Repeated retraction as some doctors recommend is repeated trauma and prevents the natural healing process just as pulling a cut open again several times a day would do. That cut would have a very high probability of becoming infected and would leave a massive scar when it eventually healed. Repeated forced retraction of the foreskin will do the exact same.