Welcome to the forum
Not sure why your lug nuts are different sizes, maybe aftermarket wheels?
Just find another lug wrench that fits & keep it with you,
or get all new ones that are all the same size.
To remove the one that you rounded off, find a 12 point socket that almost fits & beat it onto the damaged nut with a hammer.
Then use a ratchet or breaker bar to remove it.
I would suggest using a 1/2" drive socket.