fully ignoring the margin

I want to print 9 paper-"cards" out of a A4-paper piece.

Its important that they have a width of 7cm. The lenght can be among 9,9cm and 9,7cm.

So i thought it would be clever to create just a spreadsheet of 3x3 fitting a piece of paper. the inner borders are the line where you later cut out the "cards".

The margin around the edge of the paper will not be printed anyways but I need this framework for a 'perfect' cardsize.

I tried other ways, but realised excel is heavy buggy with that. I set a margin of 1cm. switched the B-colum to 7cm and the A- and C-colum to 6cm. In that way the framework should be still perfect BUT LOL switching the viewmode on excel back and forth (the 3 buttons in the bottom right corner beside the zoom) f*cked up the column size again. Try it on your won. The column sizes are changed for no reason. Even with the margin of 1cm and I reduce the column-size again about 0,0x cm on A and C excel changes it back after switching the viewmode.