I gave a too powerful magic item at too low level for a bad reason, what to do?


When a paladin in the game I run went into the local store ran by an ex adventurer, he went to the back to see the fancy swords, and asked if any looked like his holy symbol. The god he follows is illegal in that world, so I thought it would be cool if the shopkeep had one, so I narrated an old padded box that she takes out with a sword that exactly matched his holy symbol (which is a sword in a cicle). I narrated a tingling feeling when he touched it. But then I realized; he’s level two, the game has barely started, and I had him buy what seems to be a potentially extremely powerful magic item for 60 gp. I don’t want to backpedal lamely and make it weak, but it seems like a sorta dumb way to get a great item. What should I do?

To clarify, neither I nor the player know what item he has. I don’t want to make it a lame +1 sword or something, when I narraed it as something powerful. I was thinking of teiring it, at 1st teir it does nohing, second teir 1d6 extra radiant damage and +1 AC or something, add an extra d6 and armor boost per teir, by L17 itll be +3 AC an 3d6 extra radiant, but I am afraid that might be too good for something he bought and didnt even do anything to get.