That's just the nature of tunisian crochet! If you read the text in some of the posts on the different tunisian stitches, I think there is some explanation of why that happens. It's because of there being more of the yarn on the back of the fabric than on the front, so the piece naturally will roll forward. Not too much you can do about that. Even adding borders won't stop it entirely.
Glad you enjoyed the tutorial...there are plenty more there so have fun with them!