Spiraling Garter Stitch

I love to make amigurumi dolls, and I’ve made one for my brother for Christmas of his favorite TV character, the fourth Doctor (from the show Doctor Who). His scarf is super iconic so I put in a lot of effort to get it right. The problem is, I’m new at knitting and I don’t know all the tricks to make it come out right.

So here is the original scarf:
(Image from doctorwhoscarf.com, probably copyrighted by BBC or someone.)

And here is my reproduction:

The original is about… I’m not sure, probably 13 or 14 feet. My reproduction is about 37 inches long, made with garter stitch and acrylic yarn.

I’ve blocked the scarf already by wetting it slightly and then pinning it flat to dry. I thought that would take care of the spiraling, but as you can see, it didn’t. Is there anything I can do to get the scarf to lay straight?

Narrow garter stitch like that is going to spiral around while a wider one won’t. You could use the same number of sts and a larger needle - it may be shorter but not twist as much.