Duck tape is perfectly correct, it was the original name given to the tape with it only being used for duct work much later on.

From The Wikipedia article:

“Duck tape” is recorded in the Oxford English Dictionary as having been in use since 1899[2] and “duct tape” (described as “perhaps an alteration of earlier duck tape”) since 1965.[3]

It was originally used for making shoes stronger and was later used for sealing ammo tins.

But, duck tape is the original name because It was made with a duck cloth backing. “Duct tape” didn’t come into use until the 1960s.

Yeah, you can’t really take for granite these days that people spell that correctly.