In admin, i choose tools>define pages editor> and select define main_page.php..
You might try selecting the html editor for this and use the menu > insert image > function over pasting your code.

Alternatively, post your code for it is difficult to advise when all you state is:
i create an html script that links my image.. the image is there but it is not aligned
We have no idea if there is a problem in your code, your image size or what.