Hello, I Want To Ask Whether It Is Right Or

Hello, i want to ask whether it is right or not. My girlfriend's estimated period was 28th of March. Honestly, we had sex quite frequently so it can happen that the sperm could be inside of vagina. However, everytime she cleaned it within 1 minute after we finished. Anyway, I bought pregnancy test today. And it was Clearblue. It says we can check whether pregnant or not up to 4days before the expected date. And then the result was 'not pregnant'. But still I want to know that the time that we use the test is proper time? Or do we have to test again? Thank you.