Cheating is wrong in God's eyes, whether it's on a test in class, in business, in a marriage, or in any other situation. Don't lower your standards (no matter what anyone else is doing) and don't allow yourself to get into a pattern of behavior that could wreck your life.
Why is it wrong? For one thing, cheating always involves taking something that isn't really yours. In other words, when you cheat, you're stealing something that doesn't rightfully belong to you (in this case a better grade). But the Bible is clear: "You shall not steal" (Exodus 20:15). The Bible also says, "He who has been stealing must steal no longer, but must work" (Ephesians 4:28).
Cheating also involves lying, because you are falsely claiming that the work you did is yours and not someone else's. But lying is wrong, and when you lie you only end up hurting yourself in the long run. This is why the Bible says it is "better to be poor than a liar" (Proverbs 19:22).
I challenge you instead to give your life to Jesus and begin to follow Him. You may be in the minority if you do but why sacrifice your integrity and your character to follow a path that will only lead you downward? Life's greatest joy comes from knowing Christ and serving Him. Don't follow the crowd, but give yourself to Christ and discover the adventure of following Him.