new 3/8 sending unit is bottoming out in the tank?!

It helps to move around, tap one spot, move over to the next etc. If the tabs on the tank are starting to push up, that's kinda normal as those humps will push it up. It should return when you get it seated.

It's finally in, only thing left is to pray it doesn't leak thanks to all.
A quick heads up.
I bought this sink strainer lock nut wrench at Home Depot for 7 bucks and it helped.