Too early to test?

So I had unprotected sex on August 27, took a plan b the next morning. My period is now 9 days late. I took one test on 9/10 and it was negative and another on 9/15 and it was negative. I know plan B messes your cycle up, but was that too early to test to check for pregnancy? I waited till I messed my period to take the first one.