DNA ethnicity accuracy?

[Pinefamily]

So I finally got my DNA results back, after a false start and having to resubmit a sample.
My first question is how accurate are the ethnicity percentages?
All seem to match up with my research, except I'm a bit thrown by the Chinese and South East Asian percentages.
5% Southern China
1% Northern China
1% Vietnam

Second question is: are the percentages meant to add up to 100%?

Thanks.