The smooth leaves are the cotylion leaves ( I’m sure I spelled it wrong) they dont get bigger. They provide nutrients as it starts to grow and will curl down then eventually be gone after a few weeks.
The plant looks good to me. The non smooth leaves are the first set that will grow bigger.
Are you sure the other set didnt double in size making the cotylion leaves seem smaller ?
I’d do what has already been suggested and dome it. Also, back off a little on the watering.
At this stage, you only want to spray the inside of the dome lightly, since the roots are still developing and can’t take in much water. When they are this young, they get their water through the leaves. The dome will keep the humidity and heat locked in so they can drink.
The fan will help with drying out the soil and keeping the air from going stale, just make sure it’s not facing directly at your seedling.