On babycenter, there is an option to use conception date to calculate your EDD. I would use that with your O date.
You might also request an early u/s since they are pretty accurate for dating.
Wife to Andrew
Mama to Blake (4/3/08),Landon (3/30/10), Kensley (6/5/12), and our angel Nolan (6/2/15 - 6/19/15)
Expecting a rainbow in August 2016