Values i want on the X and Y axis are plotting as 2 lines

Hi, i want to graph thickness versus mass for 2 different materials (2 data points each) which seemed pretty straightforward.

For some reason it is graphing thickness and mass as the data lines instead of the 2 materials or plots the data points each as a separate line.
Tried selecting the data manually but as the Y axis isn't a constant it isn't working. Do you need to have a constant for the 2 materials for the graph to calculate correctly?

Any help would be greatly appreciated, thanks

Thank you!