According to the sentence, the one got hit by the car was Gunther. However, putting "I" as the subject of this sentence means that "I" was the one got hit. ("Having just been hit by a car" and "rushed over..." were done by the same person - "I")
So that, this sentence should be corrected, the following is an example:
<em>"Gunther had just been hit by a car, I rushed over to see if he was breathing."</em>
