This is no help to the OP but I have never had the problem with the bottom card flying off of the deck. When I first learned the deck flip I was practicing it constantly and one day, about 2 months after I first learned the deck flip, I performed the flip and the top card flew like 100 mph over to my right. It took a lot of work but I figured out what I was doing wrong and figured out how to do the top shot when I wanted to. I have used the TG Murphy deck flip with the top shot as part of my ACR and as a stand alone effect.
If you want an idea of how to turn your mistake into an effect I added my patter below.
Patter for my stand alone effect is something like this: Card handlers, over many years, have "evolved" to have something called finger tip memory. Finger tip memory, I explain, is how card handlers from the old west all the way to the card handlers of today are able to cheat so easily. Just by touch we can tell exactly where certain cards that we have already touched are in the deck. The entire time I am riffling up the back edge of the deck and dribbling and springing the cards. I also explain that me dribbling riffling and springing the cards is my way of locating their card. When I "locate" their card I explain to them that their card is about 27th from the top then I riffle again and correct myself by saying its 29th from the top. I ask them to name their card and when they do I perform the deck flip and their card flies over to my right hand face down. Reveal and watch their face its a pretty good reaction.
EDIT: If this is exposing anything please edit. I figured since this is my original patter, as far as I know, I would be able to post it.