I only got 156 but I have some objections to this finding, in addition to the only having 15 minutes to do this.
A) My claim to fame was that if you named a country, I could point it out or tell you where in the world it is, not list them all without error.
B ) This test is like school, testing how fast you know things as opposed to how well.
C) I type slowly, poorly and like a monkey.
D) I cannae speel some countries to save my life, see: Bahamas- The Bahamas (okay for this one I always thought the 'The' was official), Venezuela- Venezeula, Liechtenstein- Lichtenstein, Nicaragua- Niciragua, Philippines- Phillipines, Bosnia and Herzegovina- Herzgovina, Djibouti- Dijibouti, Comoros- Comaros, Kyrgyzstan- Kuyrgistan (Any English speaking man who can spell this off-hand, I take my hat off to you)
E) As M Two One stated, the way it indicates which things you have answered covers up some unanswered countries, I lost out on Burundi, Saint Lucia, El Salvador and Turkmenistan because of this, also had to spend precious time contemplating if the blocks cover any countries.
F) They should have Western Sahara, even if it is a dubiously claimed desert-hole.
G) I worked from left to right, saving myself the embarrasment of off-hand only remembering a handful of Polynesian states.
My claim still stands.