Should I re-pot my flowers?

Marigolds can be anywhere from 3 feet to 8 inches tall depending on the variety. One thing they all have in common though is a big root system for the size of the plant. If your pot is about 2 inches tall I'd say they will all need transplanting and the marigold probably now. Leave them and they will get root bound. I'm not surprised it was the first one to sprout. Marigolds are fast to sprout and grow