If you can't get it to retract, I would suggest removing it, it will be a little bit of a pain in the rear. Once you have removed it, you can then roll the complete retractor assy around and snap on the belt a few times while your doing that and hopefully the "Pawl" will release a tooth or two. Once you get a tooth or two released, you should be able to hold it perfectly upright and get it to retract. Remember to hold it straight upright after you get a tooth or two released or it will probably lock again and you will have to start the process over again.
eta; Don't turn on the ignition with the belt removed or the SRS light will most likely remain on until it gets reset, you could also disconnect the battery.