Using NASA's radiance calculator to make a graph to find the where the peak radiation emission are?
The graph looks correct, and after having a look at the NASA/USGS Radiance calculator, it seem that curves can't be annotated. However, below the plot there is a button to download the source data of the plot as a comma separated file (CSV), that you can open in Excel or any spreadsheet manager program and plot it with annotations and all the customization you want.

For the wavelength of the peak in emission you don't have to look further than the box below the graph titled "Wavelength of Maximum Radiance", which for the Sun should say something like 0.52 micrometers as in the screenshot below: