So scared i need some positive vibes

I found out I was pregnant nearly 3 weeks ago, I went to my doctors and they told me I was 4 weeks.. On Monday I started to bleed so went i to the hospital had bloods taken and urine samples, they sent me home after 4 hours and I returned today for a scan. The lady who performed the ultrasound said I'm only 4-5 weeks now and not 3 weeks ago due to the size of the featus. I'm currently bleeding like I'm on a period but not heavy like my usual period and have to go back in 2 weeks for another scan due to it being too small to know anything. My cervix is fully closed the sack is still in my womb, I'm still pregnant but whats going on with me? Its so terrifying, this is my first baby