Originally Posted by Watson

I usually make sure that I have no interfacing other than very basic SF101 or the like in the seam allowances when I make a bag.
Did the pouch have a lining? If so, leave yourself lots of opening room to turn the bag...it's usually an opening in the lining that you just sew up anyway, so I don't know why designers are so chincy with their measurements for the turning opening. When I stitch the opening in the lining, I stitch it like the picture attached and this gives you a nice turn to the opening when you go to close it up. (Sorry for the very basic pic...my regular graphics programme wouldn't open.)
Watson