If I have needle and thread, I'd sew it at once. I've been doing blanket stitch in situations like this, it's the easiest stitch that seemed to work well a dress or slacks can go well tacked and finished. Thanks Donna.
I have been sewing for 47 years and have hemmed many pants but lately I have found that if you use stitch witchery with a little spritz of water and a very hot iron the hem holds very well. Be sure you press the hem crease first then work the strip of stitch witchery between the fabric a little at a time. Once you have it all in then press it on both sides of the hem good. You can buy it in a roll from 1/4 inch on up. Good luck and I hope it works for you. The secret is the water and the hot iron and reading the intructions.