Need some help figuring this out!

Heather • Mommy of 💙💓💓💓💓👼👼
On February 1st I missed my period. Took a test BFP! Sadly I started bleeding on the 9th of February and my miscarriage was complete. I had another maybe Aunt flow on March 29th bleed heavy for a little over 24 hours then it stopped. Started back up on April 2nd with 2 days of light spotting. I took a test at the end of April another BFP! But I didn't know which to call my last LMP March 29th which would give me a due date of January 3rd or April 2nd which would give me a due date of January 7th. I mentioned this to my doctor and had an ultrasound at 10 weeks and they gave me a due date of January 4th. The reason I'm asking which was considered LMP is my baby is weighing behind. She would be in the 8th percentile if my due date was Jan 7th, but only the 6th if January 4th.. Which date should I use? I'm sorry if this is confusing!