Can you delay your period by worrying?

No, you cannot delay AF with worrying. The only thing you can delay is ovulation. Once that has happened, AF is inevitable!

Worrying about a late period may only delay it.

This myth is often perpetuated by the most well-meaning friends. But the reason it's not true is that stress does not delay one's menstrual period; it can only delay ovulation.

Once ovulation has occurred, the woman's body has already determined when she will menstruate. In other words, the time from ovulation to menstruation varies little from cycle to cycle.
http://www.reallifesolutions.co.uk/FORHERfertilitymyths.htm