Wait 7-10 days then see a doc if it's still there. It's probably just bruised tissue that takes a while to heal; 3 days is nothing.
In future get a rack, a bench with a rack, use dumbbells, a machine or get a spotter for a minute, so that you can continue to push to failure without something like this. Someone training alone can't ignore this and still train with intensity it'll happen again if training hard.
Not as good: use the same method but either pre-exhaust with flys so that less weight's used, or put a folded towel down to cushion the chest.