Help:u meet such racis police?

My car was hit by a car driven by a 70 year white couple from the back when I made a left turn. Except some scratches, my car was ok, but the front of their car was damaged.

Ten minutes later, the white policeman arrived and first asked lady whether I didn't turn the left light and she reponded "NO", (In fact, I turned the light on, perhpas the woman didn't see it at all or she was lying, and the third party didn't pay attention to the left light at all).

I told him I turned the left light on until the police arrived and described the accident. From the beginning to the end, the policeman was very impolite to me, and his asking tried to lead me into a disadvanged position in the accident, which was very annoying. And WHETHER I TURNED THE LEFT LIGHT is crucial in this accident.

The report will be created in two days, I don't want to see that because the reported said I didn't turn the left light on, I was liable for this accident.

Perhaps I was too sensitive about this issue, I hope someone gave me advice on what to do if such a faulty report is produced. Thanks!