Deep breaths! It's going to be ok
Winston does this every once in a while. He's got a kneecap that pops out occasionally and it takes a few steps to go back in. Sometimes after running around a bunch it pops out, but it always goes back in & the vet said that it doesn't hurt him or bother him, but to watch his weight so that way it won't get any worse.
I'd give it some time, see if he evens out ok. Definitely touch his entire leg and see if anything bothers him, but if you can't find anything, I wouldn't worry unless he has the limp still later.
Hugs to you! I know how much we all worry when it comes to our babies!