Is one rewarded for reciting Surat Al-Kahf on Friday after the Maghrib call to prayer, or for completing it on Saturday night after the Maghrib call to prayer?

The specific reward for reciting Surat Al-Kahf on Friday is granted to those who recite it before sunset. As for those who recite it after sunset, they receive the general reward for reciting the Quran. If an obstacle prevents the completion of the recitation before sunset, despite utmost diligence, then it is hoped, by Allah's grace, that the promised reward will be attained. One must be wary of obsessive thoughts (waswas) and strive against the self to be rid of them.