The Parsley, “Apiaceae”, family is very wide spread, and includes Queen Annes Lace as well as the carrot. That leaf does not look anything like ragweed, however.
Did you sow any celery seeds?
The one in the hand on the left is the confirmed parsley the OP refers to. The other leaves don’t look like celery to me, Purple.
Weeds, weeds, dam weeds
Strange and beautiful leaf spots on single weed leaf, look!
Could be ragweed
Here is a link that might be useful: Parsley family
The OP’s mystery plant has quite pointed leaflets and, although celery leaves are variable, I still don’t think that is what this plant is. I’m actually not even sure it is Apiaceae at all. Some more pictures would be useful showing the stems, the whole plant and its habit.
Help! Landscape blues and weeds
I planted a bunch of herb seeds in my tiny urban backyard garden this spring, and I thought I was growing a whole bunch of parsley until I realized it's not parsley. I ate some of it – it doesn't taste like much, but it hasn't killed me yet, either. I have stopped eating it, though. The picture has …