Congratulations on your first Twine game.
I was able to play all the way through and make it to the end. I didn’t end up testing the save/load option, but I had no technical issues with playing the game itself.
As you have noted above, the first and second halves of the game are a bit disjointed. The first half is about a kid turning 18, indulging a bit of a gambling addiction, and getting assaulted by a pair of thugs. The second half is about a fight with the undead and a cursed treasure. It did feel like these halves were from different games.
One issue I had with the story is that nothing comes of the assault and theft. Jake doesn’t pursue either justice or revenge, and the criminals do not get their comeuppance – in fact, those villains are technically rewarded in the end. Speaking of which, I was dubious that Jake would recruit Vic and Belch into his newly formed committee at the end, given that those hoodlums had literally mugged and assaulted him earlier that very day. I would’ve found it more believable if the old man told Jake that Vic and Belch were actually demons or similar forces of evil.
I liked the inclusion of the mini-games and thought they were well implemented, not only in the casino but also searching the bricks and chasing the $100 bill. (But as with the assault, nothing really comes from the $100 being found.)
I have a couple of spelling/grammatical notes:
The opening page of the game switches tenses mid-paragraph (from past to present).
Missing apostrophe: “Treasure Hunter … Jakes favorite book!” should be “… Jake’s favorite book!”
“It is his 18th birthday, afterall.” Missing space between “after all”.
Near the end of the story you mention “Werewolves and Demons.” Typically those are not capitalized nouns, and since the story does not capitalize vampire it should follow that werewolves and demons would not be capitalized either.
Again, congratulations on your first Twine game.