Rav Mendel Senderovic shlit"a has a letter printed in his sefer Atzei Besamim (38), that he sent to Rav Nota Greenblatt shlit"a asking what is the appropriate language for the shliach who brings a gett to use. The halacha demands that when a shliach delivers a gett outside of EY he must declare at the time of delivery - בפני נכתב ובפני נחתם, confirming that it was written and signed in his presence. However, what often happens is that the sofer ends up as the shliach, so the question becomes whether to stick with the precise nusach of בפני נכתב ובפני נחתם that was instituted by chazal, or modify the nusach to be אני כתבתיו ובפני נחתם which is more accurate. Rav Senderovic points out that it seems to be a dispute between the Radvaz and Panim Meiros. Rav Nota responded that his custom is to say the standard בפני נכתב ובפני נחתם then to deliver the gett into the hands of the woman, and immediately to say אני כתבתיו ובפני נחתם.
I am also in this situation quite often where I am the sofer and the shliach. I do what Rav Nota suggested and what I have seen him do (However, I didn't notice that Rav Nota was careful to say אני כתבתיו ובפני נחתם specifically after the delivery, rather he says בפני נכתב ובפני נחתם אני כתבתיו ובפני נחתם as one continuous phrase and immediately places the gett into her hands, which is what I do as well.)
There is a strong proof from the gemara on todays Daf that the language of בפני implies that it was done in your presence, but that you weren't actually the one doing it, thereby demanding a modified language so that the testimony isn't false. The gemara says that the pasuk ושחט אותה לפניו by the para aduma implies שיהא זר שוחט ואלעזר רואה. Meaning, the fact that the Torah says that it is done in the presence of Elazar implies that it is NOT done by Elazar himself, and is used as a source that the shechita of the parah doesn't need a kohein. Similarly, the language of בפני נכתב would imply that it was written by someone else in the presence of the one saying those words, but not by the person himself. Therefore it would make sense that the phrase should be modified to clearly state that the shliach himself did the writing of the gett.