Hi Elena1382,
it would of course be a good idea to ask the author of the pattern first? Or did you not have a pattern for this?
It’s hard to tell from the photo, but at least the different stitch counts in the rows stand out—that’s where I’d start (the first light-colored row of double crochets has 24 stitches; I count 25 stitches in the blue row above it). Do you always count your stitches carefully?
The correct number of turning chain stitches is also important to prevent a crochet project from turning out crooked.
As you can see, there are several possible reasons why the scarf turned out crooked.
Maybe this link will help you:
http://rescuedpawdesigns.com/2014/05/12/learn-how-to-change-colors-in-crochet/
Best regards, Marion