I commend you for your stand for Christ and your commitment to avoid lying—even when it seems like it would help you. The Bible is clear: "Each of you must put off falsehood and speak truthfully to his neighbor" (Ephesians 4:25).
Although we may think we are gaining something by lying, in reality we only hurt ourselves (and often others). When we lie, people inevitably find it out, and it makes them mistrust us and not want to be our friends. A young person who develops a pattern of lying often finds it very difficult to break the habit when they become an adult. No employer wants to hire someone whose word can't be trusted—nor for that matter would you want to marry someone who was untrustworthy.
Make it your goal to live for Christ and to honor Him by your life—including your words. Others may laugh at you, but in the long run they will respect you, and may even face their own need of Christ. Never forget: God can be trusted to keep His promises. Make His Word, the Bible, part of your life every day.
As a footnote, this casual attitude toward lying is unfortunately another sign of the moral and spiritual decay of our time. Pray for your classmates, and ask God to help you point them to Christ, who alone is "the way and the truth and the life" (John 14:6).