Welcome to the Bunnings Workshop community @toby1703. It's fantastic to have you join us, and many thanks for your question.
I'm not aware of any right or wrong side, so you are free to decide which one you prefer. However, I believe they designed it with the intention of you having the rough patterned side on top. If it is being used on a dining table, you might like to consider placing the rougher side down as it would be slightly harder to clean the food mess off than the smooth side.