Ovulation!

Hey ladies I have a couple important questions! I can not figure out .. okay so how accurate is this app?? Then my send question is if it’s accurate then why did I take an ovulation test on my suppose ovulation date the 10th and it was negative then it showed 5 days later on the 15th I was ovulating which is day 20 of my cycle .. I typed in my period normal and didn’t mess up on the dates .. do I go off my ovulation test being positive on the 15th ??? Or do I go on the 10th being my ovulation date that app is saying .. also I have 6 kids me and my husband married for 11 years and we don’t mind another one we love having a big family but I wasn’t trying to get pregnant just making sure I wasn’t ovulating before we did you know the deed lol and then it said I was when I thought i wasn’t! So confused 🤦🏻‍♀️can someone help me and tell me is the test more accurate??? Or what do I do