One thing that comes to mind is wondering if you got the bushing in there and if you do if you have it in right. Also if you used teflon tape, or some other type of sealer, RTV Silicone, etc? You will also want to make sure that the connection is not on to tight or not tight enough, when it comes to water pressure this can be finicky. You might also want to check your nut to make sure it is not cracked. One otehr thing I have noticed the last time I did some plumbing at my in-laws house is that a 5/8 would fit around a 1/2 inch and seem to work or rather tighten on like it should, however since it is really not he same size it leaves room for water to spray out of, so do make sure you have the right fittings.