I accidentally scheduled a contact list, how do I remove It?

Go to Manage Contacts, then click Contact Lists

Under "status", you'll see a small green bar. Press it to disable the sendout. It will be saved automatically. 

When disabling a scheduled list it means it won't be sent to the contacts in that batch. If you want to enable the sendout again, just press the green bar once more.

If you want to delete the scheduled sendout, click the edit symbol and then the red delete symbol. 

Notice that you can't enable the sendout after deleting it. However, you can reschedule the list again by going to Schedule Sending and then choosing the list from the scroll-down.