Baby measuring small?

Hello ladies I'm looking for POSITIVE STORIES ONLY as I'm already stressed out as it is. I went for my 12 week ultrasound and I was measuring at 11 weeks 1 day (4.3 cm/43 mm). Genetically baby is completely normal as everything came back normal/negative. My nurse said we'll have to see what the next ultrasound shows but it's normal for dates to be a bit off sometimes. I have been measuring perfectly until now. Am I doing something wrong? Looking for POSITIVE outcomes only. Thank you