Congrats, I wouldn't have guessed you are pre HRT from your profile pic.
If you are certain that you want to transition then I'm not sure I see the point in not going full time and doing your internship as who you really are. I'd imagine that in your industry people will be more interested in your ability than your gender, they certainly are in mine, (CGI, a similarly young-ish industry). And with you being young and good looking it will be less of an issue.
It is scary, I'd be more surprised if you weren't scared in some way, but it gets less so as the changes come, trust me. 🙂