Celtic Lady: A belated welcome to the forums!
Yes, your calculations are correct.
Apparently, you were born on a Friday, the 13th.
There are traditions/superstitions associated with Friday the 13th which are probably related to Judeo-Christian concepts & others.
The number 13 is thought by some to be "unlucky" or "bad luck". Judas Iscariot was the 13th apostle; the one who betrayed Jesus, leading to his capture.
"Mem", the 13th letter of the Hebrew alphabet, represents the feminine principle; Mother; birth, life, death & resurrection.
Numerologically, 13 refers to cycles, endings & beginnings. Conversely, it refers to mis-use, danger.
In the Tarot concept, 13 is Death; however, it generally does not refer to physical death, but to transformation; metamorphosis (as in from caterpillar to butterfly); the shedding or the discarding of an old life for a new one.