Ovulation date changed

So last night I got my LH surge positive :) and then when I put in today’s info the ovulation date changed I got a negative LH surge today. The positive last night said in box have sex within 48 to up your chance of pregnancy:) but then the app tells me thuraday was my 32.5 chance, Friday was my 21.5 chance and today is only 7.9 chance :(. I figured the positive LH surge meant I would have higher chance yesterday and today :/. Confused

Anyone have advice or guidance???