Hi Serhii - there are two ways to solve this. 1. bucket users as close to the exposure as possible - ie, on the Product page. 2. If that is unavoidable, you can use activation metrics to filter out from the experiment results, and only include users who saw the activation event (in this case, the event would be ‘viewed product page’).
Since the assignments are random, it is unlikely to bias your sample by those amounts. We have built in SRM checks to alert you about any significant imbalances.