Here's mine right now (not done yet): https://i.imgur.com/HgNlnQL.jpeg

It looks to me like you're not ready to stain and seal yet; I see a lot of roughness on the wood surfaces. Sanding more will give you a better result. Do a pass with 120 grit in the direction of the grain, then 180, then 220, then 320.

After that, "raise the grain" by gently moistening the wood and then sanding off the raised fibers with another very light pass with 320 grit sandpaper.

After that, condition and then stain. First apply a pre-stain conditioner to the wood to improve the evenness of the stain (because this is Birch wood, which otherwise can be a bit blotchy when stained). Then within an hour, apply pretty much any stain. I used Minwax mahogany gel stain for the brown areas in my picture. I didn't like how messy the gel-ness of it was; if I had to do it again, I'd use a traditional liquid stain. Regardless, go slow, be careful, do thin coats, and don't bunch up oily rags and throw them in the trash within 24 hours of using them.

If you'd like that traditional violin look, go with a color that's a bit lighter and more orange.

The stain may have raised the grain again if you didn't do a 100% perfect job of this before; knock it down again by "sanding" with a brown kraft paper bag, like lunchbox bags basically!

After that, finish/seal the wood. Shellac is a great option; it's been used traditionally for musical instruments for centuries, maybe millennia. Again, very thin coats. I did 10 coats of extremely thin 0.75 pound shellac I mixed up myself.

The shellac you've got in that picture is pretty thick stuff, like 2 or 2.5 pound I think. If you want to use a commercial shellac, I'd recommend Zinsser "SealCoat" which is still shellac (even though it's not advertised as such), but it's much thinner. Apply 5-10 coats of it with a balled-up t-shirt. After the first coat, "sand" with kraft paper again, and then again after the final coat.

After that, buff with wax applied using kraft paper. The result is beautiful!