Ultrasound question.

I made 12 weeks on Thursday. I went for my first ultrasound at 8 weeks. I go back to doctor next Thursday so I'll be 13 weeks.

The Nurse called me yesterday & asked why I was scheduled for an ultrasound. I said I don't know cause you guys did that. She said I don't need one and they will cancel my appointment because my insurance company won't pay for it.

Okay, this is my first pregnancy so I'm new to all of this. How will they know everything is okay? How will they know my baby didn't die or anything like that? How do they know there is still a heartbeat? I assumed they do an ultrasound since I'll be starting my 2nd trimester.

Am I crazy here? Sorry. Any advice would be great.

Thanks.