I’m sorry OP. Are you physically OK? Same with any passengers—are they OK? Once you cash the check, you agree to the settlement amount, so if you have injuries, get them assessed. Also, if you had a car seat, buy a replacement, and send the receipt to the insurance company—they will reimburse for the seat.
Some ideas: get the blue book value of your car. You’ll have options of certain possible transaction prices. Go with the highest (should be buying from a dealer). Then go online to find the car(s) closest to replacing yours, make a PDF of the listing in case you need it to negotiate.
Finally, depending on what damage was done, if you really want your car, you can take the $20k (or whatever the estimate was), and have the car repaired yourself. I did that once when I had a situation of a very low mileage but older car. I was allowed to keep my rental until the damage was repaired too. I used an independent mechanic and body shop instead of the dealership that insurance used for the estimate, and ended up breaking even. It was a little bit of a hassle, but it’s an option.