Grid help please!

Hi there! I’ve been working on my portfolio for a while and I have 3 project pages, all with the same header; a grid with a mockup, title & a short caption.

I don’t know why but I’ve had a LOT of difficulty making it bigger as I want the mockup to be bigger but then the other elements move around. Today, it sized down by itself and I looked at my automatic back-ups but there were no differences.

Anyone know how to fix this, or create a better layout in the grid?

Here is my site Read-Only: