I had my period I used a ovulating app and I had sex that day now I think I may be pregnant

No ovulating app is 100% accurate, it's a guesstimate.

You take a test at least 1 week after you miss a period, preferably 2.

Ovulating apps are useless. To truly track ovulation you need to take your basal temperature daily for at least 6 months (1 year is better) and correctly track when you ovulate.

Apps judge based on when the average woman menstruates and therefore likely ovulates (which is not a sure thing). It's a best guess, and a bad one.

Having said that, any time you have sex, pregnancy is possible.

How late is your period?