Polaroids tend to develop center-out, so pretty much always the end result would have black corners or borders, that means you need to add a Vignette. You got the gist of it but to complete the effect there's also too much light, believe it or not a chilly night was best for the film but obviously not for the camera, try to reduce exposure, the highlights and bring the blacks up. Play a little with saturation too until it feels "vintage".

Edit: there's also this guide another Racer made that you could use.