Dear Professor [name],
My name is [Preferred name], and I will be attending your course [blank] on [days] at [time] this [term]. I am transgender and have not yet legally changed my name. On your roster is my legal name, [Legal name]. I would greatly appreciate it if you refer to me as [Preferred name] and use [pronouns] when referring to me. Thank you for your understanding, and I look forward to starting your course next week.
Sincerely,
~[Preferred name]