I disagree that a plug is necessarily temporary. I wouldn't race on it, but unless it was a huge hole, it should hold.
I would check using a soapy solution to make sure the plug is where you're losing the air.
A few days after replacing an unfixable tire, I was surprised to see that the it was totally flat again after being parked. I used a leak detector solution and found that air was actually leaking from the valve stem, which I guess just didn't seal back up correctly after the swap.