Hi,
Yes if you are using gausn then par[0] will represent the area of the gaussian component, so basically the area under the peak - background.
If you want the background are, you would need to fit with a normalised background function.
There is a class in ROOT that does it automatically for you, TF1NormSum. See the tutorial
https://root.cern.ch/doc/master/fitNormSum_8C.html
Best regards
Lorenzo