I've just had a similar situation occur over on WEBTOON; I'd set myself a goal of gaining 1000 subs by the end of 2021. Pretty ambitious, but up until a week ago I had a shade under 400, so I was on track to achieve that goal, or at least come close.
Then, my comic was put on the front page. I blew past that target within two days, and now I'm pretty close to doubling it. It's fantastic, I couldn't be happier, but I'm also wondering what on Earth my next goal should be! I have a very small social media presence, so I can't expect that level of growth to continue off my own promotion efforts.
(I also had something similar happen on Tapas, which took me from about 50 subs to around 180 subs in a week, so both sites have been pretty generous to me.)
My approach to this is to just... set reasonable targets for continued growth, on the presumption that I don't get promoted again this year. So, 2.2k for WEBTOON, and maybe 300 for Tapas.
But, more importantly than that, is to simply keep creating the story that people subbed to enjoy! Which is something I intend to keep doing for the next five years, at least. Just keep creating, and sharing your work with your audience. 