Critical Angle of Glass Lab: Is My Graph Wrong?

[lionely]

Homework Statement

I'm doing a lab, and I plotted a graph for the refractive index I got about 38.3 degrees
and the material I'm working with is a glass block from reading two textbooks I came to the conclusion my graph might be wrong =/, because the critical angle for glass in air is 42 degrees. So is my graph wrong since I'm like 4 degrees off?

 

[grzz]

Are the experimetal points lying on a straight line?

 

[lionely]

Yeah I drew a line of best fit.