@JoshuaMackens, the preview tool may not show your ad for a variety of reasons. There are the obvious possible causes:
- Checking a term you don't bid on
- Paused campaign
- Suspended ads
- Incorrect geotargeting
- Bids that are too low
- etc.
A couple of less-obvious causes I've encountered:
- Ad scheduling. Let's say your ads don't run from midnight to 5am, and you use the ad preview tool at 12:15am. You won't see your ads in the preview tool, even though they're probably eligible to resume once the clock strikes 5:00.
- Device preferences. If you bid more for mobile clicks, or if you have a mobile-only campaign or a desktop-only campaign, your ad may show on one device (according to the preview tool) and not on another. Keep in mind: the preview tool shows you a mobile preview by default; be sure to check what it tells you about your ads' visibility on desktop and tablet.