A freshly squeezed lemon should do the trick, unless you overdilute the juice. I usually read about procedures applying 30% lemon juice for extraction of "active components" from plant preparations (leaf, bark, root, ...). Last time I checked the pH of a freshly squeezed lemon, it was 1.
You give no details about your preparation, so it is actually nearly impossible to evaluate the problem. So, if you expect some decent advice, tell us exactly how you performed the extraction.