So confused

Co

I just bought this brand today and thought I'd take one just to see what they're like and this is what I got problem is I had a positive opk Feb 2nd and was a week late for my period bled like normal for 3 days and then now just spotting when I usually bleed for 5 so this was taken today the supposed to be 4th day of my period when I'm only spotting any ideas as to why the strip analyzer says its positive but I have no clue as to how thats possible!