Worried help

Samantha

So I went for my first ultrasound and im.suppose to be 8weeks according to my missed period ,but when ultrasound was done doctor said I was measuring at 6weeks and 3days and wasnt able to see anything yet so I got blood work done to see.for my hcg levels and have another ultrasound appointment on Tuesday I'm worried I could be having a miscarriage any thoughts or has this happen to anyone and positive outcomes anything ??????😥😣