worried. fingers crossed, praying

ladies I have a question, I ask these questions because I dont remember my 1st pregnancy which was 26 years ago. I'm pregnant right now, with my LMP I should be 8 weeks 6 days, today at my ultrasound baby measured 6 weeks 3 days, no heartbeat was detected.. Dr said it may be too early.. I remember the day I think implantation happened. on mothers day, I was on my way back to new Mexico from Texas, I remember cramping like if I was going to start my period. could I have ovulated late, implanted at that time and my measurement be right, or am I wishing too hard. any advice would be greatly appreciated, I dont wanna think miscarriage, I'm not ready to give up just yet.