Once I've found the treasure, what do I do

Hint 1 of 6:

You should have bought something from the shop keeper that will help.

Hint 2 of 6:

More specifically, you should have the shovel.

Hint 3 of 6:

What do you have a shovel for?

Hint 4 of 6:

"X" marks the spot.

Hint 5 of 6:

Just use your shovel on the "X."

Hint 6 of 6:

Make sure to bring the T-shirt to the important pirates.