First time filer - paycheck appears as Single while I'm married

Hello,

One more question that I forgot to ask:-

I am married with two kids. On my Employee's Withholding Certificate, I chose "Single or Married filing separately" as this is the only option that allowed me to choose Married filing separately. My husband was not working at that time, and I didn't know that someone who doesn't have income needs to file.

However, on my paycheck , my filling status appears as Single. Can I still file as Married jointly? I am a bit confused; please advise. Thank you so much!