I enjoyed this, and am giving it a 3 out of 5. It could easily be a 4 with some revision, and by expanding on the story could very well reach a perfect 5 rating.
Here are some observations:
You seem more in your element when you were describing the more sinister scenes. The opening entries seem thin compared to what comes afterwards, but I suspect you were thinking readers would just want to get on with it, which isn't a surprising thought in this day and age. However if that is the case then I have to disagree. You should celebrate your writing, don't shorten it out of concern some people may not have an attention span. Put your writing out there and make people read. Don't dumb anything down.
I would stay away from ending death scenes with jabs and barbs, such as 'What did you think would happen?' Let your death scenes be enjoyable and make the reader smile and wonder what he or she should do differently, rather than admonishing them for doing something that is a part of the game. Often readers will want to choose a certain action even though they know it may lead to death, just to see what awaits them. Let them enjoy that, it's why you put it in there so don't lessen its impact.
There was a small typo when you go back to get your jacket: 'By the time YOUR reach the pathway entrance'.
There were a couple of scenes that felt abstract just to be abstract, but you had a good number of scenes that felt just right. There is a real mindscrew moment in the penultimate scene that I won't mention so as not to spoil things for anyone reading this. It worked very well and is a big payoff.
The ending was abrupt and could certainly be drawn out or put across cleaner, and as you mention the whole gamebook is short, but I think there is a lot to go on here and it could easily be expanded and made even better. I particularly think the sinkhole scene has a lot of potential and should be given more of a chance to shine.
Overall a great job, especially considering it was your first attempt at writing a gamebook. I'm not sure if you are still active on the site, but you should keep up the good work, as you have quite a bit of potential and I would love to see more.