R.I.C.E.
rest, ice, compression, elevation. for the first week. 3-4 times a day.
then after the first week - alternate treatments of ice for 15 min. per hour, and then moist heat for 15 min. per hour.
I wouldn't recommend forcibly stretching it right now. If there are any micro tears you will be developing scar tissue in the area. It needs to heal with rest.
Your normal range of motion movements should be enough to prevent it from stiffening up.
That swelling needs to reduce. I've had your injury before, it took awhile before I was back in the game.
Set the time aside to heal properly.
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Right now I'm dealing with a tendon injury that has put the brakes on everything.
I'm in Fisherman Hell staring at a garage full of equipment, kayak, and skiff.