Knit panels don't match up for afghan

I am knitting this afghan,

I just finished my third cable panel and they just don’t match up. They each seem to have an inch or so difference. I guess i’m not very good at keeping the same tension. One is even a few inches too long. will I have to reknit another panel? I have never blocked before, is it just a matter of blocking? I used merino wool as suggested and same knitting needles.

Cabled patterns do relax quite a bit when you wash and block them. I’d wet them and lay them out to dry at the same length, or as close as possible. You know, stretch if it needs to be stretched, avoid stretching if that will help it to match. You can be flexible.

That afghan is beautiful, but I know only to well the frustration of different lengths on individual panels. I’ve actually resorted to knitting the panels, [as well as both sleeves when making sweaters], at the same time on long round needles just to try to keep them even. Sometimes I luck out, but I, too, have a problem with my tension and wish I could find a way to train myself to knit more evenly.
Hope the blocking helps.