My youngest brother was also a “surprise bonus”. He is the only one of us who now actually lives in Mom’s hometown. He is there in case of an emergency. Mom has told me how glad she is that she had my youngest sibling… Planned or unplanned, what counts is being loved. OP, I trust that your parents love you.

Why would any parent tell their kid they were an accident?

I was an adult when my dad told me his first words when he found out my mom was pregnant with me were “oh shit.” Anyhow, OPs case is worse because that sounds suspiciously like what in many places would be called sexual assault.