Moses Lake Police shared a video recently saying they see this mistake all the time. Despite your best efforts, you could be endangering your child:

The rule is knowing the weight limits on the anchor restraint belts. The LATCH systems in cars (anchors in the car where belts on the car seats can latch onto) are easier and safer than the seat belts. But the anchors are only good for up to 20-25 pounds INCLUDING the car seat. That means they should only be used for very small children.

Fred Goldstein