Hi Mark. Nice job starting out, you'll find it a very rewarding experience! Yeah, it looks overexposed to me too and that burns out the detail. Attached are the spectra of some stars, just taken with a SA & a NexImage webcam. No great shakes, among the first shots I did, but you can see a lot of lines that burn out when you overexpose. The bars at the bottom are done by cropping a section along the spectrum, reducing it to one or two pixels height, then expanding it to 20 or 30 pixels height.
Keep up the good work & keep posting your results!
Cheers -