My results are different from my original poster title now. How I should prepare the poster?
Of course you shouldn't pretend that the result is still significant, when you know now that it isn't. As you have noted, that would certainly be unethical.

Prepare your poster using the results that you believe are correct now. If anyone asks about the difference between the poster and the abstract, just explain what happened. (You aren't the first to make a mistake and catch it later, nor will you be the last.)  You can also email the conference organizers to find out if they can update the poster title and abstract (online at least).

Occasional mistakes are common in science, as in everything else; don't stress about it too much, just learn from it for the future. It's great that you caught it now, before your poster presentation, so that you can correct it.