UV unrawpp keep getting bent >< I honestly don't know how fix this problem:
I have modeled a cola can. 
I created seams in all the right places. (at list as far as i know.)

and unwrapped the UV
and while they are no distortions on the map. the islands for some reason comes out bent when they should be in a streight line.


so any ideas about what to do?
you could you use this addon:

https://github.com/Radivarig/UvSquares

it is made for this specific purpose. While the addon is free you can consider supporting the developer if you like and use it: 

https://blendermarket.com/products/uv-squares/

for how to use it:
https://www.youtube.com/watch?v=VYZnGIql2UI