Sounds like costochondritis.
That airbag has a lot of energy and it can bruise the chest. I've seen people develop black and blue marks. An x-ray is generally negaitive. There is no specific treatment except time.
It should eventually go away. It may take a long time.
Motrin will help.
Sometimes sleeping with slight pressure on the rib helps, as well as warm compresses.
eventually will go away, the pain its from the impact, muscles get very sore after it's been hit, specially an airbag has suck an impulse, it takes a while, if your not allergic to advil, ibuprofen, any pain reliever will help it might take a good month or more until you feel even better. sorry that happen to you.
Welcome to the MedHelp forum!
Caregiver has given some excellent suggestions. Try warm compress, analgesic creams and see if it helps. If you have breathlessness or cough or the pain increases on and off, then another CT scan should be done to see if there is a clot or injury that was missed earlier, since it was a high impact injury.
I would be comfortable if you could get yourself assessed by a doctor.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!