First of all, unprotected sex on 2nd day of period is very much safe and there is no chance of pregnancy
at all. So you have nothing to worry here.
2nd thing, if you missed one pill, you must take 2 pills immediately after remember or next day and continue rest as per schedule. Combined OCP
has highest effectiveness (around 99.9%) in preventing unwanted pregnancy if you take regularly on scheduled time.
Be well & take care.