The first two are fine (if you end the first one with a period). The last one should, especially in formal conversation/writing, read: "It looked like it was going to end poorly." Here, you are working with adverbs (end well). "Well" is the adverb which modifies the verb "end." The most common antonym (opposite word) for "well" is "poorly," and is also an adverb. "Bad" is an adjective; the antonym is "good." As an adjective, it can only modify a noun; it should not be used to modify a verb (such as "end"). In informal speech, it's generally going to be OK if you use the last sentence. But it might sound unpleasant to people who are aware of the difference between "bad" and or "poorly." Still, "poorly" is not often heard in regular conversation, so it might sound awkward, even when used correctly. My advice: best to stick with sentences that use the word "well," like the first two examples you have.

You could also say "It looked like it was going to end badly." "Badly" = "poorly", but "poorly" sounds too formal and fussy (mızmız) to me.