Obvious Noobie Query

I made this thing here, using the GIMP. My original intent was to make it a header, but....I know nothing about headers. I'm using flexible squares, the dimensions of the graphic I made is 600x276 and you can view my journal here. Is there anything I need to change for my header? Is there a code I can use to make it work? Am I omitting something you need to know?
Thanks,
Lena