Ok.. by following this guide only levels until 2-1 will be hard.

When you reach chapter 2 you can easily skip every next levels by completing any previous one. (i suggest 2-1)

e.g. if you are stuck on 3-4 just go back to 2-1 and level 3-4 will count as completed so you can proceed to level 3-5.

I only suggest you doing this on 3-4 and 3-8 because these levels are impossible
If you are skipping levels just complete last one 3-12 and you will get achievement 'Full Tank'