Ketostix only measure ketonuria (ketones in urine) rather than the true measure of ketones in the bloodstream (ketonemia). Ketonuria is only an indirect measurement of ketone concentrations in the bloodstream, and ketostix measurements can be inaccurate.

Don't worry too much about it. It's kind of overwhelming at the beginning but if you keep up with the general spirit of the thing (i.e. low carb, especially as low as induction levels) then you'll be almost certain to be in ketosis.