You need to contact your buyer(s) and ask them to see what it says in their paypal accounts either: 1. Pending / Unclaimed with a cancel option. 2. Pending / Unclaimed. 3 Completed.
If its: Pending / Unclaimed with a cancel option.
Ask them to cancel the payment but tell them that it will take a few days to go back to their funding source. Then get them to use the "send money" > Goods/Services option and pay to your correct email address. They may not want to do this and so you could then cancel the transaction. OR you can send them a money request.
Pending / Unclaimed.
If there is no cancel option then the buyer will get their money back automatically 30 days after paying. Again they may not want to pay you again until they get their money back so you may need to cancel the transaction for them.