I don't use that brand, so I don't know which is the control line, but as long as the test line is lighter than the control, it is negative (test line must be as dark or darker than control line.
If you test once a day, you could miss the surge as it can be quite quick.
Also opks don't tell you if you actually ov or not - they only tell you if the LSH hormone surges (which typically inidicates you will ov in the next day or so). They only way to tell if you ov is to use bbt to track... so you might never get a positive opk, but you could get the temp spike which indicates that ov has taken place.