How far along am I?

I had a miscarriage on the 16th of December but I was told by someone to go by the first day I started bleeding as if it was a period (13th December). I don’t know when I conceived should I be entitled to an early scan? I’m in the uk so we don’t get one at 6 weeks. I’m going by the first say I started bleeding so I’d be 7+4. I’ve got midwife Friday but I was just wondering before I turn up there looking stupid