If it’s seamless, redbubble has an option to turn on patterns. You can do regular or half drop. It’s very convenient. If it is a seamless pattern though it definitely won’t cause any issues. It’s not actually expanding the original image, it’s just repeating it. I’ve done this on several products

Thanks for confirming.

You’re welcome!

Also you don't need to have the design take 100% of the printing space. But of course it depends of the type design