Need help trying to do a Gaussian fit with 3 peaks

I am working on some data, my instructor has asked me to fit Gaussian curve( y= a*exp(-((x-b)/c)^2) ) in a way (see attached file), I tried using the curve fitting app in Matlab2014b, it does give me 3 different values for parameters a,b,c but the value for parameter comes out to be negative. Is there any way I can fit the Gaussian in the curve? I have attached the data and the intended result plot.

Any help is appreciated

Answer 1

[the cyclist]

If you want to fit your data to the sum of three different gaussians, that is what is known as a gaussian mixture model. Use fitgmdist.