If that's the lettuce I think it is, it's a leaf lettuce, and your spacing should be fine.

Planting lettuce now? In zone 10 California? Good luck with that!

Dave

Dave: If the OP is on the coast, there's no problem with lettuce, except maybe a couple times a year when the famed Santa Anas come. And we "shouldn't" see any more until Late Sept/Oct. I say shouldn't because this year we got some in the Spring, which is a rarity.

Kevin

I start mine in flat then I transplant in the garden , spacing about 6-8". When they start touching, I start pulling to leave the room for other ones to get bigger. If you don't want to thin, then you can space them wider, like 10-12".