Henry: I saw her ankles.
Captain Jack Sparrow: You would've seen a lot more if you kept your cakehole shut.
Carina Smyth: Filthy Pirate.
Captain Jack Sparrow: There's no need for name calling.
Captain Salazar: Jack Sparrow... Do you know this pirate?
Henry: Only by name.
Captain Salazar: For too many years the Triangle has cursed us, condemned us to this Hell on Earth. The key to our escape is Jack Sparrow, and the compass which he holds. No, no. No need to fear, me boy. I always leave one man alive, to tell the tale. Find Sparrow for me and relay a message, from Captain Salazar.
Henry: Salazar.
Captain Salazar: Tell him I'll behold the daylight again. And on that day, death... death comes straight for him. Would you say that to him, please?
Henry: Yes.
Captain Salazar: I wish I could tell him myself, but dead men tell no tales.
Carina Smyth: I'm not looking for trouble!
Captain Jack Sparrow: What a horrible way to live.
Carina Smyth: Men on that ship are looking for Jack. And Jack is on this boat. I'm going to swim for it!
Captain Jack Sparrow: How dare you do exactly what I'd do if I were you?
Henry: Do you even have a ship, a crew... Pants?
Captain Jack Sparrow: A great pirate does not bother with such intricacies.
Captain Hector Barbossa: I have heard stores of a mighty Spanish captain who sunk and killed thousands of men...
Captain Salazar: No no no no! Men, no! Pirates.
Captain Jack Sparrow: I once knew a Spaniard named...something in Spanish.
Henry: We are to be allies!
Carina Smyth: Considering where your left hand is, I'd say we're more than that.
Carina Smyth: Who am I to you?
Captain Hector Barbossa: Treasure.
Shansa: The dead have taken command of the sea. They're searching for a girl, a Pearl, and a Sparrow.
Answer: He's probably worried that either the crew will attack or at very least frighten Henry. Or he just doesn't want Henry to see how horribly the curse can affect people.
But because Will is ferrying souls to the after life, like Davy Jones should have done for the full time, he was captain of the Dutchman. There is no curse that would make the men look like sea monsters. They only started to look like that because Jones denied his duties after 10 years of service, when Calipso didn't show up. So the crew would look like normal men, so Will being worried that Henry will be frightened by them, can't be the reason he started to panic.