I just did a binding with a 3" strip (Ironed folded in half) because I wanted it to be wider in front. I used a 1/2" seam instead of 1/4". I did get a little gapping between the hand stitching on the back, but I think it's only noticeable to me. I'm pretty sure I get that to some degree on all of my bindings.

I just re-read this - are you saying that you sew the top of the binding down my machine, but when you try to bring the binging over to the back it doesn't quite reach far enough to cover the stitches from the front?

Let me tell you this much - sew about 3" of your binding down and test the fold over to make sure it's gonna work and be full. (You definitely don't want it to be hollow.) Most people recommend a 1/4" seam on the front when sewing the binding down. If you want it wider on the front, you can, just test different sizes of seams and widths of strips on scraps.

Question, are you sure 4inches was the binding width and not the border width have you miss read the instructions.

Im not meaning to be rude but it is difficult without a picture

If the quilt police were to show up they would give you a bad time about that gap! Otherwise known as quilt show judges. Lol. Personally I would take it off and re cut it to 2.5 or 2.25. Lots of work but you will be happier with the quilt.

4" sounds like a LOT too wide. I use between 2-1/4 and 2-1/2"...that's plenty, unless you are intentionally making extra wide binding. Look at the pattern picture of the finished quilt...what does the binding look like? What does the pattern say?

Just fold the edge on the back under before you sew it down. That fold will help to bulk up your binding so no gap. If you can't judge by eye how much to fold under, iron a crease in it before you start.

4 inches is pretty huge, I cut mine 2.25 and set my needle position on 6.5. I always sew a few inches and make sure I have a true .25 inch seam , fold it over and check that its even on top and bottom.
Then, press with iron to set the seam, then press it back flat, fold and press again, then I VERY lightly glue baste. Then hand sew the back down.

This is how I learned to do bindings:

http://www.youtube.com/watch?v=a2hWQ5-ZccE

wow-that is a really wide binding! did you pull it down on the back until it was tight & smooth? i would think a binding that wide would be an extra border feature-
usually if you use a 2 1/2" binding strip- fold in half+ 1 1/4"
stitch to front with 1/4" seam-fold over it is just enough to cover the stitching line on the back= 4" would give you 2" extra to fold over on the back.
just folding it over to cover the stitches would leave it flapping in the wind for about 2" worth???

If you are going to put it in a show I'd say , you don't want that extra space inside the binding. But I would take it off and cut the binding strip down. I cut all of my bindings 1 7/8 inches the fold in half, sew at a scant 1/4 inch and turn to the back and with my hidden binding stitch I have NO space in my binding and it is 1/4 inch on front and back.

Thank you Steady Stitching for posting that great tutorial.