so the first time future twilight already existed as future twilight who had theoretically already went through all the events past twilight was going to go through?
It's all one timeline
The warning we saw at the beginning of the episode was for Twilight not to worry about anything, but both her and us believed it was a warning of a great disaster
Twilight realized at the end that nothing bad happened, so she went back in time to warn herself, only to fill the place of the warning we already saw and close the circle
Of course, there's still a paradox because Twilight had to go back in time to start the events that lead up to her time traveling
Time travel is a very tricky subject, but this situation is a little more explainable than most