Hi Alejandro,
You can either use the shortcut PS (for peak symbols) to move between/cycle through four different types of peak symbols or if you open the SpectrumDisplay Settings you can set your peak symbols there. Also right-click / Customise should show you the cycle peak symbols (PS) option.
There is a description of the different peak symbol types here: Customising Peak Labels
Basically, once you have fit your peak the ellipse is drawn at the half-height of the peak. So this is a good way to check that the fitting is a good fit: the ellipse should basically fit nicely into the contours. If that isn’t the case you should redo the fit. I find that the starting parameters do affect the fitting, so occasionally you have a play around a bit where your peak started (SE and then RG often works well). And if there are peaks that are close to one another/overlapped, you should use the group fitting routine, RG. You will probably see that the fits improve.
Best wishes,
Vicky