Any return that has not been successfully sent via NETFILE will show as "In Progress".
Yes, you can delete the return you are currently working on. If you have other returns in your account, select “View All Tax Returns” from under “My Returns”, and delete the unwanted return by clicking the small Trash Can next to it (or “Delete” under the return name). If there is no trash can next to the return that you want to delete, then open another return. Now when you go back to “My Returns” you should be able to delete the unwanted return.
If this is the only return in your account, you’ll need to start a new return, before you can delete your existing one. To start a new return, select “Start a New Return” from under “My Returns”. Once you have started your new return, you can select “View All Tax Returns” from under “My Returns” and delete the unwanted return by clicking the small Trash Can next to it (or “Delete” under the return name).