In the public release of the game, you're supposed to go talk to jason before going for the baking soda. This was unintented because you're supposed to be able to do anything in the game without him. So, yeah, this is corrected in the latest build but in the public version you'll have to talk to him for now.
You need to have completed the mansion and talked to jason about what to do next. To do that you have to open the backroom in your house. The key is in your backyard, behind a pushable crate so you need to find the push skill in the haunted house.
That skill can be found in both way, left or right depend of your maturity level.
Hey,
The backroom being open or not shouldn't prevent you for continuing the game. If you're lost, don't hesitate to check the walkthrough here ;
https://board.net/p/PaciProjectWalkthrough
Cheers