Oh no, this is not the beginning. My aim with this game has always been a duration of at least 4 hours. If it ends with more play time, then that’s good, but it won't be a 10-hour game.
To answer your question.
Using build 6 (which is currently only available for members of Patreon but is the build with the latest content). The main story is around 40% done, and the erotic scenes are around 30%.
I’m still debating whether I should add some of the scenes that were suggested by a few players, but if we stick to the plan, these are the percentages.