Cbfm detecting pregnancy?

[Emw4783]

This is my second month using cbfm. I usually ovulate on day 20-21 and I have a 32-33 day cycle. This month, I was high from days 11-27. I thought I might have missed my peak. We bd on days 16, 18, 20, 22, and 24. We stopped because we figured I had already ovulated. Well, today is day 28 and it showed a peak. I'm expecting my period in 4-5 days. What could that mean? Am I really ovulating this late? I took a hpt and it came out negative. Is it too early to test for pregnancy? Could it be a false negative? I'm so confused! Any insight would be appreciated. Thanks!