April TTC

So I just got my period yesterday, a little emotional, and a little upset....
Another disappointment, but I have to pick myself up off the ground a try again next month.
Below is my projected fertility calendar for April. My last period was 2/28 and then today 3/27. I believe I ovulated on 3/13 of this month.
With the calendar below, when should I start having sex? Yes I understand every other day is good... When are my most important days??
How can I guarantee my chances next month?