In Montreal you can go to any police station and they will take a look at it to see if it’s in properly…it a free service, not sure about other places…
You can go to the local Fire Department to check on it. Google it and you will find out who in your neighborhood checks the proper positioning of the car seats.
My local police department (Ramapo) had a specially trained officer who showed me how to install it. You want to push the car seat down into the car’s seat as much as possible – he suggested I put my knee on the seat to use my body weight to hold it down.