Can't remember when my last period was. Can I just take a pregnancy test 15 days after the ?

I had when I was ovulating (I know I was ovulating as I have an ovuation counter). I don't have irregular periods but am usually have about a 29-31 day cycle. Now the took place 15 days ago so is it alright to take a pregnancy test? It would be fine if I got one of those early detection tests but I picked up the wrong kind and it says you "can test as early as the day after your missed period". But I don't know when my period was as I did not take a record