Cadence while climbing

Hello,

I have trouble with my cadence when im climbing in Zwift. It shows around 30-40 rpm but I counted it too around 80-90. Can I fix this somehow? Does the cadence affect my speed uphill or is it just the Watt? 

I use a Bkool smart pro, and I do not have a seperate cadence meter or a garmin. 

Thank you!