Small zipper issues

Ugh!  I don't know what's wrong with me.  For the life of me I can't seem to sew the zippers correctly for a small coin purse.  AHHHH!!  I've made several and they all seem off. 

Since I dove in and cut into my first set of vintage sheets (late last week for the apron giveaway) I've been attempting to make some coin purses from the same set of sheets.  For the price I figure it's good practice fabric, and there is just so much of it. 

You can't see it here, but the green one has a gap where I failed to cover the zipper opening, and the top right one doesn't zip close all the way.  :-(

Ok back to my issue.  I think my issue is that the zippers are 4" zippers.  I've gone through about a dozen tutorials, which are all similar one way or another and the finished product looks clean and finished (in the tutorials), but my end results are ..... uh wonky? Plus the tutorials use zippers that are much longer then cut them down. Maybe that's my solution.... use much longer zippers.

See the top left one...the zipper is bowing.  The blue one you can see that the fabric is puckered at the corner.

I didn't have any issues with a 9" zipper.  Look at the cute little purse I made out of half a place mat.  The zipper was easy to install and the whole project was super quick.  So why can't the small coin purse be the same?

Place mat purse.  There is the whole place mat, the other half is cut up and ready to make another one, and my finished purse.

You can see the reverse side of the mat inside of the purse. 

This place mat purse was inspired by another purse I have that I love to use on the weekends.  Especially if we are going to festivals or open air markets.  Big enough for my phone, cash, keys, the occasional small purchase or water bottle.  When out with my kids I prefer a purse that I can wear that crosses over my chest.  This way I have both hands free, and not have to worry about putting my purse down and forgetting it somewhere. 

My inspiration purse.
(I had a hard time getting the camera to focus on all these pics...I'm just having issues all around.)

Wow! Talk about easily distracted...I'm wanting to complain about my 4" zipper issues and then get off track.  I'm not sure what is going on with these coin purses.  Maybe I need to revert to bias tape.  I made my sister a cute coin purse for Christmas that used bias tape around the edge.  It's just that I tend to fight with bias tape as well.  My bias tape maker has been used 3 times since I purchased it in January, and each and every time I've used it I fail to some extent.  What happens here is that the bias tape doesn't fold correctly at the seams where the strips are joined.

Maybe coin purses are not meant to be my thing.  We'll see...eventually.  Who will win?  Me or the coin purses?