I screwed up my calender

So I have only been using this app for about a month. I love it. I have been trying for a very long time to get pregnant, or not preventing it anyway. But I had sex on my last most fertile day, my period was supposed to start today. It has not. I'm not running out to buy a pregnancy test or even getting my hopes up yet. However I was trying to edit my period and ended up moving it to where I start on the 4th. How do I move it back or should I just leave it and go by what I already know. Who knows? I may end up starting on the 4th. Please ....prayers that this time is the ONE!!