Again, I agree with Madonna and how she handles it on her forms.
As long as you weren't conducting business while you were in the US and can honestly put 0's in the columns for "time spent on business" and "amount earned in the US" don't bother recomputing anything.
If you were in the US for more than 30 days and you're relying on the physical presence test, you might have some difficulty. But if in doubt, do it the way that benefits you and see if the IRS comes back at you for your "mistake." (It depends on how big a difference it makes in your taxes due.)
Cheers,
Bev