The timer is in the wrong place
Automatic spots are fixed per timer type: the end of the Add to cart form for a product timer, the top or bottom of the page for a bar, the top of the page content for a landing timer, and the top of the cart and cart drawer for a cart timer. There is no margin to adjust on them.
For anywhere else, set the timer to Custom position and place the app block. The block renders exactly where it sits among your theme sections, so move the block rather than adding space around it.
It looks different from the preview
The preview and the storefront use the same rendering code, so a difference usually comes from the font. System fonts only show if the shopper device has them installed, and otherwise fall back. The bundled web fonts load wherever the timer shows, and Use your theme fonts follows your theme.
A background image has to be in your Shopify Files, which is where the app uploads it. A suggested image from the library is imported there too.
Bars and the page around them
A bottom bar pads the bottom of the page by its own height, so it does not cover your footer. Sticky is an option for a top bar only. If your theme has its own announcement bar, decide which one carries the message while the timer runs.
The timer is added once the page has loaded, so on some themes the content below it moves down a little as it appears. In our measurement on Horizon, layout shift was the same with and without the app. If it is noticeable on your theme, send us the URL.
The storefront shows an old version
A publish reaches your storefront after a short delay. Reload, then try a private window to rule out your own browser, then clear any page cache app in front of your storefront. For a per visitor countdown, remember an edit starts every visitor again, which can look like the old timer coming back.