What would happen if a U.S marine patrol was attacked by a scorpion the size of a large truck?

Step 1: Run away from it as fast as possible because that thing is scary as heck.

Step 2: Regroup and hit it with rockets, grenades etc. (alternatively call in an airstrike or artillery strike on it if possible)

Step 3: Approach it slowly and shoot it with rifles to make sure it's actually dead.

Step 4: Call the scientists to study whatever is left of it.

Impossible for anything with an exoskeleton to be that large

The scorpion would get killed that's about it

They probably would just try to kill it then send a few biologists to look at it.

they bit*h slap you to your awake and stop having such silly dreams