Double post problem is not because of your template but it might have happened when you tried to change the blog template. When you upload a new template for your blog ,Blogger ask you whether you want to delete these widgets or choose to keep it. This option is useful but the problem arises when the Blog1 widget and Blog2 Widget clashes. Blog1 and Blog2 are post widget so the post will appear double.
In-order to fix this problem. You have to delete a line of code Follow my steps:
Note: Remember to backup your template before editing the code.
1) Go to edit HTML
2) Find the below code
3) Just delete the second code
That’s it 🙂 hope your problem is solved