Pat yourself on the back for a good job!
That will look pretty.
However, the pattern you are using (k2p2) is a rib pattern and rib patterns are notorious for pulling in and being elastic. That's what ribs are meant to do and that's why they are great for collars, cuffs and the bottoms of sweaters.
I don't think you will be able to block it any wider than it is already because of all the acrylic in the yarn you are using. It needs to be a natural fiber to really block. Otherwise it will just pull back to it's original shape.
If you are really bugged about the width you might want to consider starting over with more cast on stitches. Frogging your work (rip-it, rip-it) is part of the learning experience for even the most seasoned of knitters. We have all had to do it at some time or another.
But if you are ok with the way the scarf is coming out, knit on.