F M L .
Fun fact: TGoM started as a third-person story, which I converted to first-person prior to publishing because I'm a fucking moron.
I need to go reread Demesne and Pirene and figure out how the fuck they did it.
Heh. Demesne. Pirene. That rhymes.
Really? You can have internal thoughts in narration. I mean, the function of the past tense assumes that the character exists in an unspecified present and is relating to us, the reader, what has already happened. Besides, the flow of text isn't literally a character's inner monologue; the things you "think" are distinct from the general fuzz of awareness you have that only appears in stories as linear text by way of convenience. If I tell you "I hope she understands what I'm getting at, I thought," you understand perfectly well what I mean.
So yeah, all the text in a first-person story can be inner monologue, especially in the present tense, but that's usually the writer deliberately playing with the form and isn't expected to be the standard. I use italics to denote specific thoughts and no one's ever complained. Don't worry about it.
If everyone always stuck to the writing guidelines down to the letter, fanfiction would be much more boring. Don't confine yourself and try to spread your wings.
Of course, that's not to say you should drop everything and start the Swan Song style of writing, (although, why not) but don't sweat over the small stuff.
Yeah, there's nothing wrong with a first-person narrator stating what she was thinking at that point in time. Italics are the way to do it.
Alphacat is wrong. It's not all interior monologue. It's the character telling you, the reader, after the fact, what happened from her point of view. To repeat, what happened includes interior monologue—which may or may not be reliably presented to the reader.
Swan, we love you. Just keep doing what you do. I'd be thrilled to be able to write a third as well as you do.
If you were trying to get this published-published, and not just writing fanfiction, it might be worth worrying about. But here? Meh. Your story is better written than 99% of the fics here (in my opinion) and has a concept I'm fairly certain I've not seen play out in this fandom yet.
So just keep the train going and, as Zaid said, don't sweat the small stuff.
The things you find searching for your own fics on FimFic.
2752023 ...Huh.
I guess that's one way to get senpai to notice me? xD