Whether it is correct to write in English as "GAyatri"?

It is गायत्री ---- ईकारान्तः

In English we have to distinguish between GAyatri and GAyatrI .

Some people use GAyatree .

In Transliteration , it has to be written as Gāyatrī

Anyhow, it should end with ई and that is important.

जय जय श्रीराधे