Most of the calculators, including mine, are not very accurate at figuring PH changes when the TA if way off of what they assume.
Adding the entire box of borax won't be a significant problem. The PH should be reasonable for now. By the time you add a couple of rounds of baking soda the PH will end up a little too high and will need to be lowered slightly.
Remember, every pool is different. None of the calculators can tell you exactly what will happen when a chemical is added. So it is best to add a little less than you calculate you need, let it mix in, and test the water to see where you are.
Adding the entire box of borax won't be a significant problem. The PH should be reasonable for now. By the time you add a couple of rounds of baking soda the PH will end up a little too high and will need to be lowered slightly.
Remember, every pool is different. None of the calculators can tell you exactly what will happen when a chemical is added. So it is best to add a little less than you calculate you need, let it mix in, and test the water to see where you are.