Nervous

On Tuesday I am teaching a lesson on problem solving using measurement. The students are being asked to each take on a specific role in a group as well as figure out what the perimeter of a fence is on a worksheet. I am kinda nervous about the outcome, they have been involved in groups like this before, where they are receiving no help and have to figure out everything on their own and work together to do this. Hopefully everything goes as planned and they understand how to find the perimeter.
Wish me luck.