Help!!!

Joanne
Ladies, need some help here...
My LP was 13 November and I ovulated between 23November and 1december, I got a BFP on 13december which as of today would make me approx 8 weeks pregnant, my scan is showing I'm measuring 5weeks which would take me back to the week after I ovulated! Took a digital test which showed 2-3 weeks which makes me 5 weeks but none of the dates match my LP or ovulation so I'm starting to panick! 
Has this happened to anyone?!?