I'm a physics newb and I'm trying to find the index of refraction of water. The pic is my setup from the top down. The blue lines are the sides of my container of water and and the yellow lines are the paths of the light ray. I found the angle of incidence to be 40 degrees and the angle of refraction to be 28. So using Snell's law, I found that the index of refraction for my container of water is 2.75. But the index of refraction for water is supposed to be 1,33. So did I fuck up with my procedure or are the sides of the plastic container refracting the water? I think it's the latter but it could be both. I was planning on adding a solute to the water and seeing if the index changed but i can't do that now as i can't even get the normal index correct. Is there a way to mitigate the effects of the plastic? Or do I just have to give up and try a different procedure?