Hey Mahen,
that’s because you only mentioned the blog posts page and thus my customization was intended only for that template. To make the single posts also stretch to full width of the content, please add some more CSS:
.single-post #main #content { width: auto; }
and upload the contents of this archive into your theme folder.
Let me know if this achieves your desired effect!
Sincerely,
Andrew / Satori Studio