Has it gone back yet?
If not, see your doctor. You may have what is called paraphimosis. You need to get the foreskin back as it can actually cut off the blood supply to the penis.
It's normal for it not to pull back until you're about 16 or so. Don't ever force it.
Again, see your doctor.
Paraphimosis is the name of the condition of a retracted foreskin that is stuck behind the glans penis (head) of the penis and will not go forward. One can read about paraphimosis on the Internet.
If the foreskin is tight enough it can cut off blood circulation to the head and cause edema (swelling due to fluid accumulation). Paraphimosis should be promptly reduced when it occurs. Paraphimosis may be reduced by squeezing the head of the penis really hard to force the blood to leave the head. This will temporarily reduce the size of the head at which time the foreskin may be brought forward.
If attempts to reduce the paraphimosis are unsuccessful, then one should go to the emergency room of a nearby hospital. It is not necessary or advisable to be circumcised although some old-fashioned doctors are likely to recommend it.