Use the instruction manual when threading the seat harness to be sure the straps are in the right slots for your child and the harness is threaded correctly. The harness should be snug against your child's chest and the harness clip should be at armpit level. The seat should be secured very tight in the vehicle with the locking clip properly used if it is needed. Refer to the vehicle and car seat owners manuals to determine if a locking clip is needed and how to use it. Never use a seat that has been involved in a crash.
Car seats are a single use item.