Alright so, you were not suppose to use your dirtbike in the the sewer. In the siege of fort papa, when you were still on the pirate ship outside of the fort, you were suppose to go into the ships hold and get the deployable shark spawn. The shark you spawn with that you can ride and you were suppose to ride it into the caves under the fort. Brickbeard even told you this was the plan, I am assuming you did the parkour glitch where you fell from the mast in front of a cannon going off launching you into the fort. If you went through the caves you would have known you were suppose to spawn it in the sewers and the other sharks wouldn't attack you as you were protected by your shark. At the end of the caves you were suppose to get a yellow key to go up into the fort. But since you got into the fort via glitch you never got the key.
Edit: So I am in Jetpuff's Towers and I am stuck on the bridge between the two towers. Every time I attempt to go across the patrolling guard somehow always manages to see and throw a spear at me. Are you suppose to go across the bottom of the bridge or just be really persistent in not getting caught?