Yes, if you don't hit your pre-order goal, you can end your campaign. If you've already collected payments with your backers, you may need to refund those payments, however, to avoid refunds, first you need to set your Payment Capture settings to 'Manually' so that payments are not captured automatically when your backers pre-order, instead, those payments will be Authorized for a specific duration called Authorization period, beyond this period, the hold on those payments will be released, in that case it's not considered a refund.
We recommend that you create a campaign with the commits phase enabled. Commits enables your backers to reserve their order by submitting their email, no payments are required during the Commits phase. If you hit your commits goal, the pre-order phase starts automtically or manually, it's up to you. When pre-order phase starts, all committers will receive an email notification to let them know the pre-order phase has started.
Hitting your commits goal is a very good indicator that you're going to hit your pre-order goal, it's always a good idea to keep your commits goal a little higher than your pre-order goal.
If you don't want to start taking pre-orders automatically when you hit your commits goal, you need to disable the "Start the pre-orders phase when the target number of commits is reached" checkbox; what this does is give you control over when you start taking pre-orders and when you're happy with how many commits you got.
Send an email to firstname.lastname@example.org