Witness to a trial

Has anyone been a witness to a trial? I witnessed a car accident back in January and I asked one of the cops if one of the victims was okay and the cop pulled me to the side to write a witness statement. I did not know that the victim died therefore making it a murder case. Anyway the lawyer issued me a subpoena because I did NOT want to testify especially if this lady’s family is going to be there. Im scared for my safety and although this lady killed someone, I do not be apart of the reason to put anyone behind bars. Has anyone been a witness before and how many times did they call you to court? Was it a one time thing? Im concerned for my safety.