Okay, so I reloaded, which landed me on day 95. I stacked my defenses on the castle's row and won. Final score 41800.
Yes, I lost my castle, which gave me some kind of defeat screen with a score, but after I got a victory screen with a different score. After a few screens (an epilogue screen, a thank you screen, etc), I was back at the main menu. I chose to reload, replayed the game from day 95 onward and successfully protected my castle, after which I also got a victory screen.