Now I'm confused, how does drywall come into play? Sure hope you did not use it behind the tile board.
Wrong tub if there's no lips one the back sides.
Really need a picture to try and figure out what it is your trying to do.
No box store I know of is going to cut the tile board for you.
A hack saw is for cutting metal and drilling a row of holes is not even close to the right way to do this.

Now I'm confused, how does drywall come into play? Sure hope you did not use it behind the tile board.
Wrong tub if there's no lips one the back sides.
Really need a picture to try and figure out what it is your trying to do.
No box store I know of is going to cut the tile board for you.
A hack saw is for cutting metal and drilling a row of holes is not even close to the right way to do this.

no I did not use it behind the cement board around the bath tub area.
The tub is the original tub installed in house. It has about an 1/8" lip but that is really not sufficient since the tub is lower by about a 1/2" on the wall side. I am not physically strong enough to replace the tub.
I dont know of any other way to cut cement board other than taking it back to home depot and having them do it. But you say that they wont do that for you. So I'll have to call them and find out. Like I said earlier I am trying to do the best that I can by myself. I live in Houston and contractors are really trying to screw me on the prices of everything and some of them wanted to put sheetrock behind the cement board. Not one of them said anything about the flashing on the low side. So I am trying to get the best info I can to proceed. Thats why I signed up on this website. And I do appreciate the help that I am getting here.