Well, yeah, you're being at least a little paranoid. I haven't heard much about the DDC being wrong. There is some stuff floating around on the web, but mostly it's just old impossible-to-confirm stuff. Some might be written by trolls and some might be legitimate for other reasons than lab mistakes (such as, someone sent his buddy in to do the DNA test in his place), and maybe one or two stories are right but those I've seen are pretty old. The DDC does a huge number of DNA tests a year, and if it was wrong even one in a thousand times, you'd see a lot of chat about that online. Instead you see a person writing their story, and lots of people repeating the story and embroidering on it and telling about their fears. Gossip motivated by fear is not more accurate than a lab test; and you had a real lab test from a legitimate lab.
Regarding pinpointing the conception to the day after you ovulated and you feel this is somehow a big problem, first of all, your ob/gyn doesn't know the exact day when you ovulated. He or she was adding a standard 14 days to the date when your period began. This is an average, it was not a date whispered into the doctor's ear by the Lord who knows all things including the details of your personal ovulation cycle.
You also imply that if you ovulated on the 29th, this rules out sex on the 30th as producing the pregnancy. It doesn't. The egg can last floating around in your body for 24-36 hours, still viable, before being impregnated by a sperm. So, even if it had been out of the ovary and floating down your tubes to the uterus for a day before sex on the 30th, getting pregnant then is a total possibility.
I don't know what to tell you about your anxiety except that it's pretty common for women who only test with one of the two men to freak out. They think the expensive prenatal DNA test will solve all their problems (and I'd say it did, in your case). But then they start obsessing and saying "what if? what if? what if?" Psychiatrists call this excessive rumination, and it's a bad idea to ever do it to yourself.
If you think it will stop you from doing this, get another DNA test with the other guy. (Incidentally, why *didn't* you test with both men? One guy's test would have confirmed the other's and maybe you wouldn't be doing this to yourself now.) Anyway, consider testing again if you think you won't just keep going "what if the test is --- WRONG?!?!?!" if you have two results that confirm each other, just the same way you're doing now. Or, get sensible and realize you got a 99.9% answer from one of the two best labs in the world for prenatal DNA testing, and calm down. I don't see your result as being wrong.