First, be absolutely sure of your timing, triple check all 5 important marks. Check all of the rest of the work you just did. Check for fuel, check for spark.....
Then, I would suggest plugging in the "poop loop" (diagnostic connectors under the dash) and scan for codes (maybe cam sensor, crank sensor etc. not plugged in tight) If it doesn't show codes, the last thing I would suspect is that one of the teeth on the crank gear is missing (the little ones that the crank sensor detects, not the ones that the belt goes on)
Hope this helps