As you can see there is one really dark area because of the adjustment you've just done.

To fix it grab the Brush Tool (B), select some soft round brush and pick the black color. Now click on the thumbnail of the Levels layer and start painting over the circled area. The adjustment becomes invisible.

Step 4 - Adjusting the Right Wall

The right part of the wall should be darker too. Add new adjustment layer Levels above the layer RIGHT BEND and set is as shown below.

Create Clipping mask from the layer. You may notice that the adjustment layer adjust also bottom part of the wall.

You need to hide the adjustment from this part because we will take care about the bottom part in next step and it would not work if one part is darker than another. You hide the adjustment same way as in the previous step. Grab the Brush Tool (B), select soft round brush, pick the black color, click on the thumbnail of the adjustment layer you've just added and paint over the areas you want to make lighter.