Is it overly formal to say 南开大学 (Nánkāi Dàxué) "Nankai University" instead of its abbreviation 南大 to people at 南开大学? This is a sentence I wrote on WeChat to another teacher at Nankai University:


  可是我不是一个学生。我是南开大学的教师。
  But I'm not a student.  I'm a teacher at Nankai University.
  (Kěshì wǒ bùshì yīgè xuéshēng. Wǒ shì Nánkāi Dàxué de jiàoshī.)


I'm worried that saying 南开大学 instead of the shortened version 南大 (Nándà) is too formal.  (Analogous to saying 中华人民共和国 "The People's Republic of China" instead of simply 中国 "China".)

Question: Is it overly formal to say 南开大学 instead of its abbreviation 南大 to people at 南开大学?

I asked some Chinese friends, but I didn't get a precise response.  They pointed out that 南大 is often used as an abbreviation for 南京大学 (Nánjīng Dàxué) "Nanjing University" (nowhere near Nankai University, in Tianjin), but when two people are actually at 南开大学, there's not much of a risk of confusion.
Unlike 中华人民共和国, the name of “南开大学” does not carry that level of formalness. It is alright to use it in conversation.

And the short form of "南开大学" is usually "南开", at least that is the one I always heard. You can use "南开" to make it more casual. This is what we often use to refer to "南开大学" in conversation.

(The wikipedia page of 南开大学 has such a note:


  《南开大学章程》中明确：南开大学的简称为“南开”。在民国时期，南开大学曾简称“南大”。目前，在天津等地区南开大学仍时常被简称为“南大”。


)

And by the way, in casual talk, I would use "老师" instead of "教师"