Chance of false positive?

So, I had taken a blue equate test and it started off so faint that I thought I was imagining it. After 3 minutes it was more noticeable but still so light that you could barely see it. I showed my sister and she said its "so common" for blue tests to look like that and be false. 10 minutes later the evap made it darker and she said that even more shows its false..

What are the chances?..

Should I just wait and use a FRER before getting all discouraged?