Paid incorrectly 😠😡

So basically ever since telling my boss I am pregnant ( she was happy for me btw) she has hired someone new, cut a shift that I had next Saturday and now I check my pay slip and I’m under paid by a whole shift. Not happy at all. I told her I am able to work up until I’m due or up until doctor says I can, so upset as we really need 2 incomes right now... 😓😥 what can I do?