Hello: Stuff happens, but when changing the thermocouple, did you take apart the pilot as well? If you removed the pilot tube from the pilot burner, the orifice could have been lost. (it looks like a very small, cup shaped piece of metal with a tiny hole through the middle) If you didn’t undo the pilot tube, the orifice couldn’t have gone walking.
When I replace a thermocouple, it’s usually easiest to remove the whole burner assembly from the gas control, slide it out, work on it with some elbow room and then replace it.
It may sound a bit strange, but I plan to stay in control of any job because water, gas and electricity seem to enjoy their freedom and like to get loose! 😉