LMP vs U/S measurement.

Leslie

My last period was May 6, 2018 so I should be 6w2d but my first ultrasound measured me at 5w4d. I’m worried this could mean miscarriage. I’ve already had one and I’m not prepared for another. My fiancé said if we lose this one we should just look into adopting and I’m not opposed to the idea but I’m also not ready to give up so quickly. Anybody else measure less than what they were supposed to and have a healthy full term pregnancy?