All the new leaf growth comes from the center. Your semp actually is not looking all that bad as far as health. The curling leaves is from not enough sun, also the pale color is from not enough sun. Is the soil wet from top to bottom? You can take the rosette out of the soil and check the roots for rot and what condition the soil is in. When you do water just water the soil, not the leaves. When you take it up take a photo of the roots for us.
