Is there a calculation error when figuring my refund after entering estimated taxes. The amount of refund was figured by subtracting the amount of refund I had from the estimate I entered instead of adding the two together. Why?

Your estimated payments are not added to your refund.  Your withholdings, estimated payments, and various credits are added together, lines 25D and 26 and 32, for total payments on line 33.  Total payments are subtracted from total taxes on line 24 for the Refund

or...unless the original value was actually a "Balance Due""....i.e. the extra you owed at that point in your tax  preparation..