Hi Amanda, welcome back to the community.
Just to make sure, your 2D mesh uses a different domain than your 1D mesh, right? I see that you use your my_geometry for your 2D mesh.domain size, while in 1D, you use (30.0, 107.0,- 88.0) to (64.0, 120.6, 88.0). because this domain size will affect the number of particles being scored to your tally bin. the bigger domain size will give you more particles within it, and that is where you need to know your mesh volume to calculate the average flux in that mesh.
Have you checked your calculated tally with some metric that you already know? i.e. Have you checked whether the total power of your model is equal to the power if you already knew the power? or using your source strength or total number of particles? Sometimes we just need to do some checks just to make sure that we have proper input for our case. maybe this discussion could help you