Hi Mahesh,
if you are planning to opt for a twin sharing trip and going alone then you have to pay some amount. Tripoto have announced this options for twin sharing trips as lots of people wants to take their friends and family of free trips, so this options allows them to take the second person for a discounted price. If you want to redeem it for one person then you will have to pay as well.
Yes, you will have to pay extra amount as the points you've redeemed are for your booking but you have to pay for the person that you are taking along with you.