Colours changing when i exported a gif

trader-reggie-walk-cycle-pixilart (1)-export


so i made this pixel art on the website and i exported it as a gif to put into asesprite.
then when i did all the colours started flickering, and i had a bunch of unused colours in the palette thing on the side.
and i looked it up and alot of people were talking about the colour limit, but there was only about 20 colours in the original artwork, and it seemed asesprite added all these random ones.
just wondering if there was anyone who could help me solve the problem for the future.

hi, everwren! can you post original file which looked correctly?