Brief Answer:
Too small an impact to cause a concussion.

Detailed Answer:
I read your question carefully and I understand your concern.

I am assuming that you do not suffer from any disease which can affect coagulation like advanced liver disease or some born coagulation defect.

In that case I would agree with your physician, judging from that description that type of hit causes too minor an impact to be a cause of brain injury in a young healthy person like yourself. Some minor injury to the skin and muscles which are at the surface is possible, it will heal gradually if present by itself, but the brain itself is protected by the skull and should not have sustained any damage. There is no sudden violent displacement of the head either which might be another mechanism of damage, so you should be alright.

I remain at your disposal for further questions

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Brief Answer:
Read below.

Detailed Answer:
Small accidents happen to most of us at one time or the other, me included. It is precisely because of that that our most vital organs like the brain and the heart are situated behind strong protective barriers like the skull and thoracic cage, in order to be well protected.
So it would take a trauma of a much bigger magnitude to cause damage, either a direct strong hit with skull fracture, or a hit which involves a sudden violent movement causing the brain to impact against the inner surface of the skull, or its nerve fibers to overstretch and get damaged (the last two most probable in your car accident).
Such an episode as you describe seems insufficient to cause any of those phenomena I mention. It is natural for to worry easily considering your past history it is legitimate to experience some anxiety when head trauma is considered, but I think you should try to relax as you should be fine.

I hope to have been of help.

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