Yeah, It's because of pixel ratio. Probably you have Macbook or other higher density screen and this result in larger bitmap.
I have fixed it locally already, update will be deployed next weekend.
That's it, it's on a Mac. Thank you for your incredible work !
I was thinking of something else : would it be possible to choose a font through a file upload button ? The tool appears to be made on Construct, right ?
Good news, I've added file input button. Looks it works.