I strongly suspect that at some point you had identified yourself by your boyfriend's last name. Ihave seen it happen many, many, MANY times with GFs holding themselves out as married and using their BF's last name.
If you fail to appear for the subpoena, it might be possible that the court could order your arrest. yeah,you might be able to sort it out later, but, you'd still have some time in the pokey.
It might simply be best to appear in court and tell the truth rather than try to get cute and dodge the appearance.