This may not explain your discrepancy, but since it's come up in the comments. Check your owners manual to confirm proper oil level check procedures. Some manufacturers recommend a warm engine rather than cold for an oil level check, and the car's dipstick is designed for that (with the hashmarks/lines designed for taking into account the hot oil will have expanded versus a cold check)
The 2018 Mazda 3 4 door/5 door manual instructs a warm oil level check (not sure if this is the same as the 'hatch')
1. Be sure the vehicle is on a level surface.
2. Warm up the engine to normal operating temperature.
3. Turn it off and wait at least 5 minutes for the oil to return to the oil pan.
4. Pull out the dipstick, wipe it clean, and reinsert it fully
https://www.mazdausa.com/siteassets...18/mazda3-4door/2018-mazda3-owners-manual.pdf