@AndrewLittle 

Canvas does not understand the terms preparation and assessment, it must be told that they are worth 30% and 70%.

1. Click on the Assignments link in the course navigation menu.
2. From the Assignments page, click the Assignment Settings (3 vertical dots) at the top.
3. Select Assignment Groups Weight
4. Check the box to weight final grade based on assignment groups
5. Specify the weights
6. Click Save

If you need more explanation, see the How do I weight the final course grade based on assignment groups? page from the Canvas Instructor Guide.