It's normal for your foreskin to be tight and not retract until about 16 or so. Keep working on stretching it. You can get an erection and pull down on the shaft skin so that the glans (head) spreads the opening OR you could spread the opening with your fingers. Skin grows by stretching. Don't hurt yourself but you might feel some discomfort - the more you do it the faster it will get loose.
4" is normal for a 14-15 year old. Some guys get big early and others later. Don't compare yourself to others.
Hope it helps.