Why Don't The Check Register and Trial Balance Match?

Checks entered as “to be printed” are calculated into the Check Register balance, but are not calculated into the financial report balances like the General Ledger and Trial Balance.

To find unprinted checks, you can change the view in your Account Register to Unprinted, or you can sort your Account Register by the Prt column.  

You can also use the print checks screen, select the desired account and any unprinted checks will show up there.