What if I find out I submit to a wrong category?

What if I find out I submitted to a wrong category? Is there a
way I withdraw the submission?

Do I re-submit to the new one I think is a better fit?
Thanks.

If you think you submitted to the wrong category, make sure you identified the correct one and submit one more time to the best place. Don't submit everywhere slightly related, though - see the FAQ for further information on this.

Btw: If it was only slightly wrong (like there is a subcategory you didn't see the first time, that would fit better) you might as well leave it to the editor to sort it out. Sites are routinely moved to better places when submissions don't arrive in the best place.