Bravo!
That's pretty hefty for a first leaf so far, even for the first leaf from a tiny seed bulb. Although, the monadelphum and szovitsianum species do seem to grow larger tiny seed bulbs than other Lilium spp., in my experiences so far. I'm pretty sure I remember that they only grow one leaf this first season above ground.
How deep is the pot, and how deep did you plant the seed bulb?