initial credit card reconciliation - forget to set opening balance

trying to reconcile a credit card for the first time, but the card has been used for over a year

I set up the c/c payable account, but left the balance as 0.00 because I had not yet seen the c/c statement

I recorded a transaction for 122.33 (example), and started the reconciliation - per the statement the starting balance is 300.00, the ending is 422.33 - which I entered in the bank rec and cleared the transaction - so the unresolved is / should be 0.00

but I'm left with a discrepancy of -300.00 and an unresolved of 300.00 - no matter why I try under 'add prior outstanding  I can't make both 0.00

what am I missing ?