The left side (nut halfway down the threads) is ok, right?

It looks odd that the strut sticks up so far. I suspect they mismarked the part and you actually have the wrong part from KYB, or the part is defective.

Ride height is determined by your springs, so the struts won't matter.

I think you're gonna have to get a new strut. Can you exchange it?

To get the nut off, you're gonna have to grip the strut and just wrench it. Otherwise, you'll have to torch cut the nut off.