You pushed to soon no doubt. If you hit where yo siad it could have been a little too far back that said he probably will expire but if you push one too soon he can live a lot longer then you think. I have saw deer hit in the heart run for several hundres yards if pushed. If possible go back and look in the last place you found blood and start in a small circle ever extending it look under brush and tall grass. You would be surprised how easily they can hide even while dying.