Coding problem

I have an issue with accessing my site after trying to code a pay pal button to the site. i accidentally copied and pasted the wrong coding above the <?Php> and now it wont let me log on to access my site to edit the site and fix the coding.
Can anyone help me with this issue? how do i get in the back door to get into the coding once again?
i need a tech support and am having no luck figuring this out.