Majavelli Moe

I got a diagnostic done on my truck. It said i needed a distributor and an o2 sensor. I replaced the distributor and the truck started but won't stay on. I did everything I was told.. I set the engine at top dead center.. I liked up the simple with the white line.. I put the distributor in.. it wouldn't fall in so I bumped the engine over until it dropped into place... then I bolted everything down. Now it will only stay running as long as my foot is on the pedal.. can someone please tell me is the timing still off or could it be somthing else? Thanks in advance