WTF is up with these two-dot “ellipses” I keep seeing? How can anyone think these are ever correct? Use one dot for a period to end a sentence. Use three dots for an ellipsis to show the sentence trailing off or to show that something has been left out. Use two dots only when you want to look incompetent as a writer.
Change the position of each only (before one instead of before took) for clarity. (Technically, only is just there for emphasis in the example sentence, since only is derived from the word one anyway.)
It took only one carefully crafted spell for you to get where you are, and it would take only one to ruin you.