I've popped countless autos its totally in the realm of possible for them to start showing sex at 2 weeks. I personally like it that means that the strain has really fast genetics. It might end up being a tad bit smaller but it's hard to say because all of that is entirely strain specific. Autos will very often still grow in size while they are simultaneously flowering. Think about it this way, they flower and veg at the same time. Some auto strains do it faster than others so it's hard to say exactly how yours will turn out. I wouldn't be concerned either way.