In The Garden: What is this green goddess?

I planted this from seed in April and this is what I got. I don't think it's lettuce because the leaves have rough edges. Any ideas out there?

 

Possibly an English daisy. Is it hairy? The teeth on the edges may not be right for that, I'm not sure.

 

Thanks. I'll keep it inside to see what happens. It didn't produce any flowers yet.

 

All lettuces should produce a milky sap. So if you break a largish leaf down by the crown, you'd see at least a meniscus of milky fluid form. Doesn't mean it actually is lettuce though. This late in the season, I'd just wait for a bloom stalk. Lettuce should have bolted by now, that is, produced a flowering stalk.