What Reconcile Ending Balance are you entering?If you're reconciling to the 12/31/17 statement, you should enter the paper statement's ending (or closing) cash balance as of 12/31/17.
If transactions that you entered into your register with a 01/xx/18 (January) date have already cleared in December, you entered them incorrectly.For example, a check you wrote and mailed in December for a credit card payment due in January should have been recorded with the date when you wrote the check, not the future January due date.