It's not clear exactly what you are doing. Is this program running on a web server? Are you running it as a CGI program? Where are you writing the output file to?

If (as I suspect) you're just running the program to create a local file and then opening the file in a browser then you don't need the CGI content type header. Try removing that.

If you're running the program as a CGI program then you should be printing to STDOUT, not to a file.

But it's hard to be much help without knowing a lot more about what you are doing.