No, cremation is not wrong. The Bible does not give instructions about what to do with a body after someone has died.
When someone dies they eventually decompose and turn to dust (just as God said would happen — Gen. 3:19. Also see Ps. 104:29; Eccles. 3:20; 12:7). Cremation simply speeds this process up.
At the resurrection (Dan. 12:2; 1Cor. 15:20-23; 1Thess. 4:14-16), God will have no difficulty raising people to life whose bodies have turned to dust over thousands of years, so he will have no difficulty raising people to life whose bodies have been cremated.
Right at the beginning of the Bible God forms a human out of the dust of the ground (Gen. 2:7). This is easy for God to do. So he will be able to do it in the future when he raises people to life again.