Keep the Same spacing between images vertically/horizontally

Hello, 

I am building my portfolio and I tried to place images at the same space vertically/horizontally like the this images. ( attached image 1)

URL : https://www.youjinkim.design/

However, it is very hard to make these things happen on Squarespace. I tried to change the the gap spacing on the setting (Attached image 2) but it looks that the vertical and horizontal space between images looks same but it is not. I viewed my site on Tablet and it is not the same spacing anymore.

So can you tell me how can I fix the spacing on Squrespces ?

Thank you.