Crochet blanket edge curling

[SeymoreButts]

So I'm nearing the end of my first crochet project - a scaled down version of the Attic24 granny stripe. I've made a few mistakes with tension (namely far too tight about halfway through the blanket and too loose at the start) so it's not perfect! The blanket border is a round of treble clusters, followed by 2 rows of treble crochet, a row of single and then a picot style edge. I've got as far as the row of single crochet row and the entire border is curling up really badly. What causes this? I've done ch 2 at each corner, should I have added more chains??

[RhondaJean]

It may just need pressed. Can you lay it flat and does it sit ok eveb if you have to hold it down? Or if you flatten it is it tight/ puckers somewhere?