Hello! i  bought the app by mistake. Could you please refund the purchase?

We can't refund anything, we are fellow users (these are user forums), we obviously don't have that ability. And you shouldn't post your email address on a public forum (unless you like spam emails).

Purchases are considered final but you could try the 'report a problem' page to contact iTunes Support and see if they will refund you as a one-off : http://reportaproblem.apple.com

Or you can try contacting iTunes Support via : http://www.apple.com/support/itunes/ww