Thought I was 8 weeks 😥

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Found out I was pregnant two weeks ago and going off the first day of my last period, I would be over 8 weeks now.
I used the Clear Blue weeks indicator test to see if the weeks matched up and I'm only measuring at 2-3 weeks (which I know they say add two weeks so would actually be 4-5 weeks)
This would mean my baby is only 5 weeks and not 8 weeks? 
I have my scan in two weeks time but curious to know if anyone else had experienced this.Â