Step 1: Customize template
Go to your blogger homepage and look on the left side menu for "Template," then click on "Customize."
Step 2: Adjust Widths
Click on "Adjust Widths" on the left menu to find out how wide your entire blog is. Mine is 1010.
Step 3: Add CSS
Now click on "Advanced" on the first menu and scroll down to the bottom of the second menu where it says "Add CSS."
Step 4: Copy and Paste
Copy the following html code and paste it into the "Add CSS" box on your blog and change the number (in blue) of my width to match yours.
*Note: Don't change anything else in the code! Just the number.
Final Step: Save
Click on the orange button in the upper right-hand corner that says "Apply to Blog" and you will see it work on the blog preview.
Any questions? Requests? Didn't work? Leave a comment and let me know!