Filling the gap between wall and Vertical Blind head rail.

Hello, My first project of installing the blinds is not going well. I took wall to wall measurement and went to Home Depot and got the Home Decor premium Faux wood blinds. After coming home I realized that the vertical measurement wasn't accurate as there is a half inch tile that starts 15 inches from the top. I went and got the blinds cut. Now I noticed that the Head rail is too short and not secured well as shown in the pics. I would really appreciate if you could give me an idea how to fill the gap between the wall and the head rail. Thanks in advance.