Thanks for reaching out to us! This looks like a bit of a bug with the Mac “magic mouse” on our program version. You can overcome it right now by using our web version, however we will fix it in an update soon.
In the meantime while we work on the update, you can also avoid it by being conscious that if you scroll something, such as the effects list, then if you move over the main image straight away that zooming can carry on and zoom into the image unintentionally. So by waiting for the scrolling to stop, you can avoid it.
If you have any further questions or feedback, please let us know!
– Regards, The Ribbet Team