Sending to Nigeria is a common scam as there is no tracking once its in the country...
Have you checked your paypal account by going to paypal (not via a link in an email)?
If you've clicked a link in the payment email, before you do anything else go to the paypal site and change all your log on details and secret questions.
If your details have been changed, cancel any cards linked to the paypal account. If you have linked your bank account to the paypal account, i.e. set it up so your bank account can fund the paypal account, phone your bank to block all paypal transactions (some banks will have to change your account number, so make a note of all direct debits etc you have on that account). Once you've sorted your bank/credit cards out, notify paypal of the stolen account. They'll want faxed copies of ID.
If you didn't visit via the payment email it could still have been paid for with a stolen paypal account. If this is the case, and you leave the money sitting in your paypal account (to avoid withdrawal fees), paypal will take it back whether you've sent the camera or not.