No I'm right....
Proton = 1.67x10-27kg
Is the same value for a nuetron.
Thats already a slight error due to rounding of numbers,
We say carbon 12 is equal of 6 nuetrons + 6 protons and we don't count electons as there mass is insignificant.
So already we know that carbon 12 has a larger mass than 12u, as 'u' = 1.66x10-27 while protons and nuetrons have masses of 1.67x10-27. (were not even including electrons masses here)
Its accurate enough but when you're working with mass energy equivelances you need to try and be as precise as possible as a small difference in mass gives a large difference in energy, but this is going into the realm of Physics and is a little off topic
Were both technically right as you never really need to work in such precise detail but I thought it would be useful for the OP to know