Hey there! I'm so sorry you're having trouble TnT
Since making this asset I've switched laptops, which made for the perfect test to implement this GUI into a new Ren'Py project >w< The first attempt failed and I got to see the errors, but the second attempt was more successful!
If the error starts with "While running game code: Exception: Could not find font u'Boogaloo.ttf" you likely have your fonts folder in the wrong spot. This folder must be added to/created in the game folder (so that the file path looks like: Project Title>game>fonts).
If you're still having errors, I would then recommend copying the code from the templates and pasting it into your scripts (for gui.rpy and screens.rpy respectively). Doing so in chunks may help figure out where the issue is coming from.
Also ensure all of the assets you've dragged over from the kit are named correctly! The GUI graphics provided have the same names as the default graphics, with the exception of the "Titles" folder (which replaces the menu titles with images! The file path is called at the end of each menu screen's code block, but if you'd like to add it manually, the code looks like this:
##Uses image for menu title. pos (x,y) denotes where it appears. add "gui/titles/load-title.png" pos(70, 25) xysize(338,225)* load in load-title.png will be replaced with whatever menu title you are replacing!
ex: "gui/titles/about-title.png" pos(70, 25) xysize(338,225)
If there's still an issue, please let me know! It's possible I'm forgetting something because I'm running low on sleep right now. Despite not being very technologically adept, I would love to help make this work for you!