Alright. I know you don't know me on DA. I'm am come here to help you how to save your project.
1.open your image.
2.use a pen where you want to trace your picture.
3.if you didn't finished then save it in the next day.
4.re open you same picture you didn't finished from yesterday , then re-trace the lineart
5. don't use the pen tool (with paint tool)
6.use the other pen tool with pen with edit and pressure tool to make your line art look the same.
7. then you paint all you want.
or if you don't get it then i'll show then i'll show you what i'm talking about okay.