It may be a good idea to stretch the length of the back by stretching the hands over the top of the head in this pose above. See example.
Stretch a the arms up for 3 breaths and return to the Corpse pose then stretch the arms up again.
Do this 12 times. This is a great stretch for your whole back. Try to make sure both sides of the back are stretching evenly. You may need to stertch one more than the other.
This pose is called Savasana the Corpse pose
If the back feels a little strange stand up and shake the body lightly for 3 minutes before resting for at least 10 minutes.