Anyone that ever gave any money at all will be considered an owner and has access to all the regular project files of a paid project.
So should you consider including a Steam key and have a lot of $ 1 supporters, you should bear that in mind.
I often use the general meaning of you. I did not want to imply that you are trying to pull a scam off. I did not follow your communication and devlogs. It could have been, that you meant to have a support version akin to being subscribed on Subscribestar. Being a subscriber also does not guarantee the retail version, unless promised so in the tiers.
If you intended to sell the early access version all the time, changing the project to paid, is achieving what you want. With the side effect that people that gave you less than the file price now also have access.
If you wanted to collect support and now release a retail version, I think creating a second page that is paid and freezing this page with the last development/testing version might achieve this. Third Crisis did something like that. Though I do not remember if they collected support money on their free version.