Does the Edit button not let you select and delete it ? If not, try logging out of your account and closing the iTunes Store app via the iPad's taskbar (and possibly also do a soft-reset/reboot of the iPad), and see if it still shows when you log back in. If it does you could try contacting iTunes Support and see if they can do anything about it removing it from your download queue : https://www.apple.com/emea/support/itunes/contact.html