You can't. There are no dead ends in the game, and there is also no restarting on the same account. Don't worry: even if you make some mistakes in the beginning, you can always develop your Haven up to a higher level and fulfill all of Captain O'Malley's Tasks. Be sure to follow the instructions in the order that they're given. Otherwise, you'll slow down your Haven's development by using up your resources too fast. If this happens, just wait awhile until you collect enough to continue.
Be safe out there scourin' the seven seas, ye scallywags!