Reddit reviews Dritz 9345W Elastic Sewing Thread, White, 30-Yard

Take some thin elastic thread and duplicate stitch it into the bottom of the cuff. The more rows you do, the snugger the cuffs will become.

I think that kind of thread comes in a few different colors, so you can pick something close to the color the gloves already are for a near invisible fix. =)

Looks a good achievement to me.

You could undo the neck and redo it. But I prefer to use a bit of elastic thread, available at many knitting and sewing shops. Run two or three separate threads through the back of the stitches. Works on other knitting problems too!

You can also use a sewing machine to reshape the sides. But I don't see the need.

It looks great! Nice neat stitches (though /u/eggnogged is right about the twisted stitches).

Now you know a bit more about why checking your gauge is important for things that need to fit just right (though to be honest, usually hats are so stretchy that they fit a range of people). You can do something about this hat by buying some elastic thread and just threading it through the backs of the stitches carefully. TECHknitter shows how to do it a little way down this post about socks that fall down.

Well done!

Many of us have a reel of elastic thread in our knitting supplies, for occasions where ribbing etc isn't quite as tight as we wanted it.