Hi Pablo,
The gain and absorption graphs are looking correct, it just seems like a much lower power ASE. Have you verified that the Core radius, Er doping radius etc are all correct?
I think the difference may simply come from the different resolution bandwidths used. In your experiment on your optical spectrum analyzer what resolution bandwidth did you use? And did you use the default setting for OptiSystem?
If you are not sure what resolution bandwidth means there is another forum post on the topic at:
Let me know if this helps!