Noob question about zac's "E"

Alright don't flame me for asking this but I'm tired of being a noob... okay so I've played zac jg a lot latley and I love him but Periodically I'll go for a gank and ping that I am on the way, then I'll hold down E (I am using quick cast) long enough that the bar fills up the range meter and I'll put the mouse cursor on the location that I want to leap to, and then release E, fully expecting a top notch gank but to only end up jumping like a inch in front of me! Idk wtf i am doing wrong, and like I said it isn't always just sometimes, but i don't know what I am doing different from when i succesfully sky thru the air Or from when i make an ass of my self. Please help!! Sorry for the long post