It's not a problem at all.
'Phone the Apple Support line (it's free) with the transaction reference number from your iTunes invoice and they'll refund the full purchase price as a credit to your iTunes account. Many Members have done this and we've not yet heard of any case of a refund being refused.
In fact, it's all win for Apple, because they get to keep their cut of the original transaction and it's the Developer who has to refund the full purchase price to the customer. So it's win-win-win for Apple, they keep their cut, they get a satisfied customer who might well now buy a replacement app, for which Apple will get another cut - so you can see why they don't raise any objections...
Tim