Once the opening is wide enough, insert a wire coat hanger into the gap and use it to press the unlock button on the inside of your door.
If this doesn’t work (or if you’re worried about damaging your car or the locking mechanism), it might be best to call a locksmith to help you out. Some insurance companies offer roadside assistance packages that include locksmith services, so it’s worth checking your policy to see if your insurer can help you out.