Hey there, the aurora looks pretty cool I must say!
I can understand you're having difficulties with scales, but don't give up! That's what practice is for.
Keep trying, and if you can't add them for now, leave them out and focus on other details.
You might want to detail the eye a bit, it helps the drawing to look more dynamic and break the "monotony" usually caused by the surrounding darkness. If I draw, let's say, a gem shining in the dark, our attention will focus on the shiniest points and almost ignore the darker spots where there's nothing shown.
That's because our eyes are made to perceive, capture and elaborate the light that hits the world around us, and that's how our sight works more or less. (If I said something wrong or stupid everyone's free to correct me!)

Thank you very much for taking the time to help me again.
Very useful hint, I'll add more glow to the overall picture and of course to the eyes :)
I think about expanding the picture, so you can see more of him and the background, what do you think about that?

It would help to give the picture more breathing room, making it less "suffocating" and helping the viewer in appreciating more details.
If you can do it, then sure! Try it!

Ok i just realised... there was no winter during the lifetime of the dinosaurs...
I feel stupid. I have just drawn this background without thinking, but actually I do not want to change it.
But on the other hand it shows that I can be creative X3

I suppose you're right! Plus the environment you've drawn was an experiment, it doesn't have to be completely realistic!
For now focus on your character, you can readjust the background later if you want.
(Unlike me who draws no backgrounds at all!)