Always wear the seat belt with it correctly routed in its guide:
Wearing a seat belt without the seat belt routed in its guide is dangerous because the seat belt would not be able to provide adequate protection in an accident, which could result in serious injury.
Position the lap belt as low as possible, not on the abdominal area, then adjust the shoulder belt so that it fits snugly against your body.
Depress the button on the seat belt buckle. If the belt does not fully retract, pull it out and check for kinks or twists. Then make sure it remains untwisted as it retracts.
If a belt does not fully retract, inspect it for kinks and twists. If it is still not retracting properly, have it inspected at an Authorized Mazda Dealer.