The reason that this creates a credit memo is a little confusing but it results from the journal entry that is created as a result of recording the bounced check and the removing payment from the original invoice(s) that were meant to be paid. To resolve this credit memo issue, go into the customer center and find the payment that bounced (had NSF) and drill into it. Since you recorded a bounced check, this payment against the invoice(s) in question was removed in order for QB to re-open the invoices for payment. Now that you are in the original payment, you will see in the list of open invoices the GJ entry that QB made to record the bounced check. All you need to do is tp put a check next to that journal entry, just like you would when recording a payment next to an invoice, and this will remove the credit from your customer's account. When you now go to record a customer payment to this account, the credit will be gone.
