My first auto, Wedding Cheesecake FF

Just the Pheno most likely my guy...you're in week 3 so in another week or so she's going to hit her stretch.

Genetics. BTW, seedlings do not need "humidity domes".

Could be light, could be genetics. She is in good colour, dont see any big troubles, just let her grow, when she will reach pot verge, then they put highest gear, you almost can see as she grows every minute if all goes well. 1 and second week of flower will add more size. Dont panic, love her, some small and chubby brings more bud than tall and lanky. Fact. Enjoy !