A few drips of gas here and there aren't going to do any serious damage. Watering down likely won't accomplishing anything, after the fact.
Are you referring to a push mower or a rider? Do you have the model numbers from the product label on the unit. TroyBilt is an MTD product and the model number is normally longer than 5 digits.
The bowl nut is brass and the carb body is cast aluminum so you could have stripped the thread in either--you'll have to remove, disassemble and inspect to determine. The bowl nut can be replaced if damaged. If the threads in the carb body are stripped you will likely need a new carb.