I must admit that I too am perplexed as to how you got CO4388 (which is a legitimate codeshare flight operated by DL, and is their flight 1477) for such a low cost. I searched for one way ATL-LAX flights right after I saw your post, and could see nothing for under $400, and I looked at the airlines sites as well as in places like Orbitz and Kayak.

Very strange.

By the way, definitely take the advice in post #6...that will tell you whether you're good to go.

Another thing...CHECK THE DATE ON YOUR TICKET. I see that one way ATL-LAX flights on JULY 21 are about the price you paid!