I have a problem whit the extrude feature

Here is how you do it.

  1. Step 1:

    1. Use sketch 5 to create a split line instead of the curve you created

  2. Step 2:

    2. Use surface offset and select the new formed surfaces and the direction

  3. Step 3:

    3. Delete the original surfaces.

  4. Step 4:

    4. create a 3d sketch and use the edges around the gap

  5. Step 5:

    5. Use the 3d sketch to make a boundary surface.

    Good luck.