If you've scheduled a post for later, you can always edit it or delete it if something changes before it's sent.
Hover over the Scheduling Tools button on the left side of the Dashboard and select Scheduled Posts.
Click the Filter button at the top to choose the social account the post is scheduled to, then hover your mouse over the post menu button (three dots).
Click Edit to change the post text, social accounts or time that the post is scheduled to go out, then select either "Post Now" or "Schedule for Later" from the publish menu at the bottom of the Post Composer to save the changes.
If you need to remove the post, you can click Delete to remove the post from the scheduled post queue altogether.