Call the officer anyway
Get her advice

You don't have a peice of paper anywhere saying that the $40 was "full and final settlement" and you haven't signed such a document either.

It was a down payment on the original understanding you made in good faith - that he would replace your wheel for the actual cost.

Good faith verbal agreements can stand up in a court of law over here...

You also have the arguament of being in shock - you were the victim - your body was dealing with the stress of a near miss.

Contact the officer - she will remember - she will empathise... call her...