Getting frustrated when you're learning is perfectly normal. And yes very important to keep persevering and not give up! How long have you been learning this? If you compare your current work to your previous work, do you see the difference?
I only do mine on the app and it's very scratchy and messy and not worth showing, unlike yours which is beautiful!
Thank you for your kind words. I don't know how to do it on app but the brush is kind of fun, and it can be even messier than your app. If you try to write with a brush, you can do messy, it's ok. Also color pencils are good. I started ten month ago, after my 7th birthday.