Props probably go through more stress every flight than any other part on the drone. A light surface scrape may well be no problem. A nick is worse, a hole, as has been suggested (as still being okay) is something never to fly with.
What you can't see is a possible hairline crack that started. I'm not saying yours has this, but that is the sort of damage you can't see without a microscope. And that is what will begin to split as the prop suffers vibration and stress during flight.
A prop strike may have caused a tiny fracture that your eye can not see and during the stresses of flight and throttle inputs that could propagate and turn into a crack that will break a piece off. In flying real aircraft in questionable weather, we say it is better to be on the ground, wishing you were up there, than being up there, wishing you were on the ground.
So with the cost of your drone upper most in your mind, if something were to go wrong with a prop in flight and I could freeze time and ask you this question, just before it tumbled out of the sky and smashed to the ground, "would you like to give me $30 dollars to stop this right now, or would you just prefer to buy a new drone?", what might your answer be?
I'm guessing you would rather go with the $30 cost. So, I'll just ask you now, what value do you put on your drone? If it is less than $30 then keep flying with those props. If it is more than that, then just buy a set.