At least you were smart about it. There are only TWO reasons to move an injured person before medical help arrives.
1. The car is on fire or otherwise in imminent danger and that's real danger not perceived danger. The most common one I saw was "The car was smoking and about to catch on fire so we moved the person"...no, there was steam coming from the engine from anti-freeze dripping on it. Congratulations, you just paralyzed someone for life because you got your training from TV.
2. The person is not breathing. The risk of further injury is a moot point if the victim is going to die without CPR.
I spent 8 years as a fire rescue EMT and have seen this happen sooooo many times. People should never get their first aid skills, legal knowledge or overall educations from watching TV.
As for good Samaritan laws they are there to protect those who don't possess advanced training specific to the event, such as a librarian who took a basic first aid class or CPR training. While someone from the general public may be protected from liability (assuming there is no gross negligence), someone who is a certified EMT, nurse, doctor, police officer etc. may be liable if they don't act. The laws can be specific to individual states so there's no blanket answer. Almost certainly if an EMT, nurse, doctor, police officer etc. were to knowingly refuse or avoid the rendering of service or help they would face severe consequences from their employer. There have been many cases of these people facing legal charges for not assisting when it was reasonable to do so.