I've found that spray stach helps

Spray starch or sizing :D:D:D

I try to iron fabric like that while it is still wet. It has worked for me most of the time. Then I spray starch it. Hope it works for you.

i have heard that vinegar works in taking wrinkles out

if a fabric is really stubborn, I'll use spray starch (if handy) or lightly dampen with water to relax the wrinkle and then lightly smooth the fabric with my hands as it dries to a damp dry before ironing again.

jeeze,,,,, I have some "premuim muslin" like that... I tried everything... starch, sizing, ironing while damp , while wet, steaming.... I got it flat enough to cut , but thats all I can say!.. I'll try the vinegar.. of course I bought a # of yards of this stuff...sigh...... and it was rough and stiff as cardboard even after several washings... I'lll never buy that again... looked nice and was soft before I washed it.... grrrrrr

Try the white vinegar.

Bluteddi, I did the same thing--the muslin I bought must be made of steel. No matter what I do, can't get the wrinkles out. I also bought a lot of it---hmm, maybe that's why it was on sale at LQS. I'm going to try the vinegar method; I've done everything but lay it on the road and drive over it.
Thanks for the suggestions and for posting this thread, Nolee..

Spray starch can help but I also do have more of a problem with cheap fabric, Walmart etc.