Hey LATENATE,
First of all, I'm really glad you're having so much fun with the game! I'd be happy to try and help you out.
Since you mention max. fitness 18, I'm assuming you're not playing the new version 0.5035, where the max fitness should only be around 8.
I’d highly recommend the new version, it explains what to do next much more clearly, and the grinding is significantly toned down.
But anyway, in the current version, you can’t expand the garden any further, so unfortunately you’ve already reached the end of the demo. The same goes for the Lost Place for Liz and Nancy.
If you can’t see anything from the balcony at the neighbors’ place, try climbing out the window in your own room.
I hope that helps you a little, otherwise, just ask here again.
Best regards