Wavy hem -help!!

[JustMuddlingOn]

I've just lowered the neckline on a dress that's made of very fine fabric but where I've hemmed it it's all gone wavy and puckers out! Any idea on how to fix this? I've tried ironing out but it's not helped much, would hemming tape ironed inside to give it more structure help do you think? Supposed to be walearing to a wedding on Saturday
Thanks

What fabric is it? A stretch or knit fabric will go wavy when stretched during stitching, in which case you'd need to unlock it and start again.

Did you sew on the machine? Unstitch and do by hand.