When I was looking for what to put i did check the chanting book on Access to insight which has two one for a group and one for an individual
(When one person is asking forgiveness)
Repeat Namo... three times. Then:
[Mahāthere]* pamādena, dvārattayena kataṃ,
Sabbaṃ aparādhaṃ khamatha me bhante.
Venerable Sir, may you forgive me for any wrong I have done you out of carelessness in thought, word, or deed.
[* Mahathere is used for very senior & highly respected monks. Change it to There for somewhat less senior monks, Upajjhāye for one's preceptor, Ācariye for one's teacher, and Āyasmante for monks in general.]
Bow down & stay there while the monk says:
Ahaṃ khamāmi, tayā pi me khamitabbaṃ.
I forgive you; may you all also forgive me.
I forgive you, Venerable Sir.
The monk will then recite a blessing, after which say:
Very good, Venerable Sir.
BOW THREE TIMES
It seamed a bit pretentious to use this one as it was automatically giving forgiveness so I opted for the one above which I found here http://www.chantpali.org/closing.html#khama_yacana