Big cramp

I had one really big cramp, it felt like it was in my uterus, kind of like a bad period cramp, and then I went to bathroom to do #2(sorry tmi) . It was pretty painful so I am scared now. Technically today/tomorrow would be the start of my missed period. I found out I was pregnant before it.

I’m 4 weeks and so nervous and worried about a miscarriage. That was the only big cramp I had in the last 2-3 hours, and no bleeding so far. I just feel like I have period bloat and very(barely noticeable) dull ache. Should I be worried?