If you continue trying you for sure will achieve them sooner or later.
The hardest thing in tattooing is lining and it took me 3-4 years to learn how to properly do em with Micky Sharpz machines not with rotary.
I am sure that double lines you have already just inked on someone (if drawing in japanesse or similar style) will help a lot.
You can try doing youtube research on how to properly add lines, if you already didn't have.
Wish you luck my friend.
If there is anything you want to ask me ,message me.
All the best,cheers!