what is worrying tom though?

As soon as the Judge sets off for the duel, Tom has the will in his hands and is examining it. He is comforted to learn that he's "got the fortune again." However, he quickly returns to being distraught when he remembers that Wilson has rendered him unable to pawn the knife. Thus, he is still without an immediate source of income to pay off his outstanding debts, creating the danger of exposure should his creditors become impatient and seek out his uncle directly for payment.