If OPK test was postive day 18 and got progesterone checked day 28 and it said I didn't ovulate is there a chance it could be wrong and I could be peg?

Not really. There's always a chance of erroneous results, but they don't happen often. If your level is above around 2.0 you did ovulate, below roughly 1.5 you likely did not. If you were pregnant, your level would likely be over 5, but a pregnancy test would be positive too.