Clear blue digital ovulation kit

Tired of TTC

Hi Friends..I have started using clear blue digital ovulation kit which identifies 2 fertile days .my cycle length is 28-30 days..I got smiley symbol on 13th day and 14th day of my cycle..when I went for ultrasound on 14th day doctor said that ovulation not happened and the follicle length is 18mm ..Went I went for ultrasound on 16th day doctor told that ovulation already happened..now I am confused..please advise what's my ovulation day..😢😢