The proportion in general is pretty good. What you are missing are some dark values. Look how dark the brush and the place between the thumb and the index finger look in the photo. In you drawing there is a general grey with small variations while in the photo the range of variation is wider. The key word is contrast.

Hey @Jo Sheridan, beautiful drawing! Yeah, some people do like to challenge themselves! It's very common that we need to erase out a lot of the linework for a more realistic result, I see no problem with that. Personally, I like the high-key look of your drawing (mostly medium to light values), I think it feels light and kind of joyful, so I wouldn't say you should have necessarily used a wider range of pencils. I think the forms look nicely modeled the way the drawing is. A wider range of softer pencils might have allowed for deeper shadows and maybe a more "dramatic" effect in the result, which could have been nice too, but I think this would have been more of a personal or stylistic choice rather than a technical necessity. I see really good representation of the fingers in your final drawing, and I notice you made several adjustments regarding shape and proportion (middle finder, shape of the brush behind the thumb...) between the sketch and the final, which I think confirms my impression that you have top notch observational drawing skills. Perhaps the further hand lessons and practices in the anatomy course might help you more with the construction stage, which will then be very useful whenever you want to stray from the reference and draw from imagination. I'm pretty pleased with this too, congrats on overcoming this self-challenge!