I've noticed that when I'm making something, when I sew two things together and then do the whole flip it inside out deal (for nice edges), the fabric is too thick and doesn't fall right.

Example, I was making a poncho so I sewed two pieces of fabric together and then inverted it and sewed the opening but the fabric was too thick and it didn't look right... And I could just hem it but then it would have ugly inside and stitches would we visible as well.any ideas?

You could try pinning and gluing it, perhaps?
Or you may just need thinner material, perhaps.
I could ask my girlfriend about it when I get home, she's a seamstress and could probably give some useful tips, perhaps. Because I just had to say that word one more time.

She said that a thinner material and smaller seams, or hot iron would be the best idea, sometimes pressing the material will make it relax a bit.

Could you provide pictures? Would be able to provide much better input then!

For a really thin material you could always try cotton handkerchiefs. They're thin and if they're cotton they take dye nicely. I don't really sew but I've dyed them and used them to make bandannas, rags, bandages, scarves and things like that.

I think you're right, just too thick. May scrap it and try again with one layer. Not sure how I'm going to achieve a rounded shape like that, though... Hmm, I'll keep trying and maybe look into handkerchiefs!