I want to reduce the size of the Grid in my theme as the square boxes are looking too big could anyone tell me an easy way to change the size?
PFA
Well if you have a CSS knowledge you can do that what’s stopping you?
Sorry you are facing this issue, it would be my pleasure to help you.
Welcome to the Shopify community! 
Thanks for your good question.
Please share your site URL,
I will check out the issue and provide you a solution here.