On your account page where all your hubs are listed with their stats, click on the title of the unpublished hub.
You will go to the hub page for that hub and at the top of the page, there is the word 'Delete'.
This will enable you to delete your hub. It will still appear on your account page for around 24 hours but will have a line through it.
If you change your mind in this time period, you can undelete it again.
If not, it will disappear once the 24 hours is up.