Hello there, Thank you for reaching out!
If you are still facing the same issue after trying some basic troubleshooting steps, could you please share a recording demonstrating that the slides themselves appear zoomed in during presentation mode?
It would also be really helpful if you could let us know the name of the template you are using so that we can try to replicate the issue you are experiencing.
Regarding resizing slides, currently it’s not possible, but there is a related feature request that you might find interesting. You can check it out here: Adjustable/Custom-sized Figma Slides
Thank you for your assistance!