You can find your saved advertisement draft if you click on “my profile” and then scroll down to your advertisement section. If you click on the blue edit button next to your advertisement, you can easily go back to editing and publishing your saved draft. The red "Delete" button will delete your advertisement or advertisement draft.
Saving changed settings of your advertisement
You can always save your advertisement settings at any point as a draft to continue to edit it later on. You can save your advertisement in step 1 or step 4 of your advertisement settings. You will find a button each that says "save draft" at the bottom of the advertisement settings.
Please keep in mind that clicking on "Create Advertisement" will not direct you to your existing draft. This button can be used to create a new advertisement (from scratch or with an existing target group).