There is a certain amount of audience expectation around games in which you are deciding various elements of the MC. I realise I mention Harry duBois of Disco Elysium a lot here, but I find him a useful point of reference for a truly non-blank-slate character where there are many directions in which to turn him. He is a fully set character, but you can guide him in any number of different ways, including dying by sitting on a distressingly uncomfortable chair and such.

Some interactive fiction works in a similar way. Take Birdland and its sequels, for instance: there is a named character whom you are playing. Others may not have a pre-named character but the MC is either only customisable by name or they are not customisable at all.

Then games like those made by Choice of Games involve a blanker slate. I would not always call them an entirely blank slate: they exist within parameters of behaviour and actions. The Creme de la Creme MC cannot have secretly been a criminal before arriving at Gallatin. The Tally Ho MC is a servant. But there is a much higher degree of customisation around their traits (such as gender), skills (such as hunting ability or occult awareness), or personality (such as shyness or calmness).

In some games, these aspects may be less flexible. An MC may always have regrets about an event from their past, for example, or always despise their parents, or always be scholarly and bookish. There are plenty of games which include such inflexible elements and plenty of audiences who enjoy them.

I have two notes for you to consider.

The first is that you'll want to make sure to infuse the game with these elements strongly, grabbing the players with the story and MC so hard that players will buy into it fully and not yearn to play a shy character, for example. You may also want to make it clear when talking about the game that these fixed elements are vital to the story and the play experience because there is a certain expectation of customisability in Choice of Games games and the Twines that are inspired by that style.

The second is that it's important not to inadvertently suggest to players that flexibility might be accessible. So: if you want to present players with an MC who is always extroverted and take-charge, do not include a Shy stat or similar - it will make players confused or cross that their allegedly Shy MC is still bossing people around and taking names.

I suspect that in your case, because of coming to this realisation in the middle of writing, that your MC is currently somewhere in between customisable and set. That is an awkward place to be, because if it feels like not one or the other, players may stumble at the inconsistency. It is a little jarring to feel like the game is intended to pay attention to their MC's personality but isn't. Much more satisfying to know what's going on in either direction.

But this is entirely fine as you're in the middle of the first draft! A great deal of this draft is about discovering what the game needs and what will need changing later. So I would suggest revisiting your earlier scenes and figuring out whether you still like the idea of allowing a customisable personality - or whether you'd like to make the MC less flexible. Either may happen! There are absolutely excellent ways of writing both approaches, but I caution against trying to do a combination as it's easy to end up feeling in a not-so-satisfying limbo.

Thank you very much for your question and I hope this is helpful!