Hello mandie-wolfclane,
It's okay if you forgot to enter your opening balance, you can record it even if you've already created transactions.
- Click on the Plus icon.
- Under Other, choose Bank Deposit.
- Choose your bank account and enter the correct date.
- In the ACCOUNT field, choose Opening Balance Equity.
- Enter the amount and click on Save and Close.
You can see this article for additional reference: Enter an Opening Balance for a Bank Account.
If need anything else, please go back to this thread.