You probably mean that your abdominal muscles separated down the center of your abdomen. The medical term for this is diastasis recti. It often happens in women after they deliver a baby. In diastasis recti, the muscles stretch and pull apart during pregnancy and the efforts of childbirth. This is more likely to happen if the abdominal muscles were already weak.
Diastasis recti feels like a gap down the middle of your abdomen until you tighten the muscles, when it becomes a bulge. Usually this condition doesn't hurt. However, the damage can cause problems with coughing or urinating. The weak abdominal muscles also put you at a higher risk of back problems. Unfortunately, you can't fix the separation. But improving your abdominal strength can help the muscles work better and prevent back pain. You might find it helpful to work with a physical or occupational therapist. A therapist can develop an exercise program to get your separated abdominal muscles as strong as possible.