Not sure which heat setting you are using but maybe try a higher one if there is one. You can also try brushing out the curls a bit more and flat iron your hair in very small sections maybe one inch pieces.

I purchased a Babyliss flat iron years ago from a salon thinking it was going to be fantastic...well it wasn't. It didn't get my hair very straight and it caused too much heat damage so I returned it the next day. I had more luck with the flat iron I use now it's called the context platinum collection black series, it works well for me and I have tight spiral curls.