Is it a sin not to marry and remain single out of choice? If you feel that you don't want to marry and prefer to remain unmarried is it counted as a sin?
Getting married is a part of worship.
If you get married you have been completed half of your religion (from a quote of Rasulullah). And then if you get married and have a children , the children will help you(by making Du'a for you) after you die.
Prophet(pbuh) said "When the son of Adam dies, all his deeds come to an end, except for three: ongoing charity, beneficial knowledge or a righteous son who will pray for him.”(Muslim).
israf is prohibited; not marrying can be an israf because some genetical and psychological development was with you and people used some their time on your development and you used earth and sun etc resources on your development; if you marry you do not lose that development, you give your knowledge to your children and wife and maybe relatives of wife and genes to your children.
they say that to get married is to fulfill half your deen, so by that line we obviously know that marriage is a big thing in Islam. what @Farhan said i guess is true, but you should make Istikhaara to Allah and see what you get. Even if you are told to get married and you dont want to, still do as Allah knows best for you in this world, and the hereafter, and that is what we are all aiming for. At the end of the day. we are all judged accorrding to our niyyah (intention), but you dont want to be held accountable for something you thought was ok. so just make Istikhaara, and In Sha Allah, Allah will guide you to what is right for you :)