Continuity mistake: After Jack and his crew take Henry and Carina prisoner to lead them to the Trident, when they're aboard the Dying Gull, Jack pushes the two ladders to the ground, but when the line is cut to release the ship the ladders are still leaning up against the vessel.
Continuity mistake: While Jack argues with Gibbs during his rescue from the guillotine, in a wideshot Jack falls over two caskets which have a distinctive shape, but their direction faces the opposite way in the next closeup.
Continuity mistake: After the bald witch walks towards a wall with stars painted on them, there's a shot of Henry threatening Jack with his sword. The grip on the sword and the position of the arm are not continuous between shots.
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.