If you have access to your Google Analytics account*, you can cancel an A/B test directly in Maker anytime.
Using Maker, you can stop any experiment from the two following locations:
*Note: You must have GA permissions to stop an experiment in Maker.
via Stories Manager
First, select the story whose A/B test you'd like to cancel. Then click on More Options > * Options > A/B Experiments > STOP.
via Live Embed
You can also stop the experiment directly from the page on your site where the variants are embedded.
First, go to the page on your site with the live experiment while you're signed into Maker on another tab. Then click on the dropdown Options Menu and select Manage Experiments. After the pop-up modal has appeared on the right (you might have to click Update before this appears), click Stop on the experiments panel.