C&C Measuring help

Not sure what you mean by wasting 2 whole grid on 4 inches of total space. If you have a space for 3 grid minus 2 inches, you'll need to cover 40 inches on that side. If you only use two grids on that side, you will need something else to cover the extra 12 inches gap.

What is the exact measurements of the space you have?

Ok sorry I completely got that messed up. D: That made NO sense at all. I have 40 inches of space for the width, with is a little less than three 14" grids. Somehow that got changed in my head, and I thought I had two extra inches. But I wouldn't have to do anything about that, so the post would be useless.
I have room for about 3 1/2 grids lengthwise. I don't know the exact measurement for that, but I know there is not enough room for the full four grids. I didn't have the chance to finish my post last night and edit it. Sorry again!

You are not wasting the grids, you are using half of them. Unless you are going next to a wall and can use brackets to tie the grids to the wall, just use the grids. Their safety is never a waste.

You can overlap the grids to fit the space.

Here's an example of a cage with overlapped grids.
https://www.guineapigcagesstore.com/medium-candc-cage