The spacing on WooCommerce related products

I’m using Woo Commerce on my WordPress site and everything is lovely. The only thing that really bugs me is the related products. Everything fits nicely, three to a row, but on the related products, the third drops off the row making it look untidy.

After inspecting the source code, I’ve found it has a margin after the third item. On the actual products page, where everything fits nicely, the products have a specific first-post and last-post class (‘post’ makes me think that is probably built in by wordpress), but not on the related products.

I’ve scoured the web, and found this bit of css I could use, but it’s not working.

Can anyone more knowledgeable see if there is anything wrong with the code:

.related .products .ul > :nth-child(3n+3) { margin-right: 0 !important; }

(And now for some reason my related products seem to be randomised, not sure when that started happening, or why)

https://www.prophlebotomytraining.co.uk/product/liverpool-sep/

Thanks