yes i tried this and it works perfectly!
sadly i don't have a camera, but i've tried to draw out what i mean - let me know if it is still confusing...oh and also i've never put a picture on here before, so i hope this works!
So the dotted lines show where you have folded to form the bottom of the bag. You can also see that there is one strip folded in on each long side. Now, you have to take the red edge and make it meet the blue line by folding where the diagonal line is. You need to do this twice, one on each side of the centre line of the bottom of the bag.
Does this make sense?