You might get your period today you know! Day 4 is when I get my period too, sometimes even day 5.
This is totally normal by the way. Many women don't get their period on the first day of the placebo pills. If this is your first month, it's going to be even odder. My periods went from day 3 to day 4 over a series of months. When I took a different pill years ago as a teen, my period came on day 1. So even as one person, my period has varied on birth control.
I wouldn't stress. If you've been taking the pills correctly, then your chances of being pregnant are very very low.