I think we become confused by "mucho," and "mucho/a," and "muchos/as" because Spanish uses the same word (mucho) for the adverb "much" (or "a lot") and the adjective "many" (or "a lot of"). Native English speakers use the terms habitually, but when we're trying to speak Spanish we have to think: Am I using an adverb modifying dance ("mucho") or an adjective modifying a noun (e.g., "mucha comida" or "muchos libros"). Here, "mucho" is an adverb modifying "bailamos"--no change in ending. But, it's not instinctive . . . yet.
P.S. This explanation is an attempt to put a vague understanding into words and may confuse you even more. Perhaps a native speaker or a more advanced learner can clarify?