This isn’t a glowforge thing so much as it’s an artwork thing.
The typeface you choose will matter a lot in terms of how large each letter is in relation to each other. Do you have an example of what you’re trying to make? How close ahve you gotten so far?
Glowforge camera view is an approximation, and they don’t promise it to be any more accurate than 1/4". That being said, there is a calibration process which can help improve the camera’s accuracy:
Some people’s camera views are greatly improved after the calibration.