Yeah, I made a mistake actually. While backward pedaling, chain doesn't go to the easiest gears, it goes to the harder ones. And this happens only when I'm in easy gears, like 8-7-6. Chain never skips when I'm in harder gears like 4-3-2-1.

I still think that chain is a bit too long, so that might fix the issue. I will see my friend at the lbs today, see if I can use his tools

Thanks for replies