Is this sentence right? But think the way things will change if you make a mistake that would maybe affect everyone.is the grammar and everything correct?
There is at least one mistake in here. You would certainly have to put "of" between "think" and "the."
Beyond that, do you need this to be one sentence? I would make it into two if I were you. I would break it at "mistake." So then you could have two sentences that went "But think of the way things will change if you make a mistake. A mistake might affect everyone."
If you want to keep it as one sentence, I would suggest chainge "would maybe" to might. I don't think it's exactly wrong, it just sounds a little odd.
I would rewrite the sentence to improve it for word choice as well. Many English teachers have the word 'things' as one of their taboo words.
Try this one:
But consider how circumstances could change if a mistake was made that had far-reaching effects.
But consider how circumstances could change if a mistake that affected everyone was made.
Could a mistake with far-reaching effects for everyone change these circumstances? (or this circumstance)