As stated above, the stop margin displayed assumes that the OAT is at the flex temp. Your actual accel-stop distance will be 3% less for every 10 degrees of difference due to the difference in TAS.
Eg. ASD displayed is 2300m. Flex of 60 degrees and OAT is 20 degrees.
Actual ASD is 12% less ((60-20)/10 x 3%) so really it's 2054m giving you an extra 276m to play with.