Jes, yes, you're getting enough calories with the Zone diet. You're getting more than 900, probably more like 1200 with 11 blocks. For starters there are 3 grams of fat to every balanced block (1.5 g in the added fat block and another 1.5 g in the low fat protein block). That adds another aprox. 150 calories to your calculation. Then you also need to consider that there is a little P in some of the C cources, and perhaps a little fat, plus some P and C in the added F blocks, etc. Those additional macronutriends add to your estimated result.
That said, there's another big consideration. The caloric need statistics you posted most likely apply to a person who’s burning glucose to produce ATP. To quote Barry Sears (pg. 104, The Anti-Inflammation Zone”), “One of the more difficult concepts to get across to athletes, coaches, dieticians, and physicians is the differences between burning calories and producing ATP from calories. ATP is the chemical that is required not only for muscle contraction, but also for virtually all of our metabolism. ATP is made on an as-needed basis from either glucose of fat. Your production of ATP is far greater from a calorie of fat than from a calorie of glucose. In the Anti-Inflammation Zone you are primarily burning fat for ATP production as opposed to glucose. This means you are also making all the ATP you need, even though fewer calories are being expended. This is why diabetics, world-class athletes, or just plain normal people require fat fewer calories on the Zone Diet than calculated from the usual metabolic equations. It is because they are producing more ATP from less calories.”