Assuming you have a Personal Account, after you create the item button code, you then have to copy and paste it in your web page or site. Once you exit the button creator, the code is not saved to the PayPal Servers (saving the code to the PayPal Servers is a Business Account feature). If you didn't save the code somewhere and then exited the either the button maker or your account - all you can do is go back and recreate the code again.
