Could a college reject me just because I filled out the wrong css form?
No, but what do you mean, wrong CSS form? Isn’t there only one? Did you provide fraudulent information, or make a mistake? Your first step is to contact the college, tell them the mistake and ask how to update/change your CSS form entries.
I filled the 2018/19 form and sent it on January 14 but my application portal didn’t show that its received and then I find out I filled the wrong year form. Since then 2 colleges sent me a rejection. Is it because the css?
When you say “rejection” do you mean admissions rejection, or denial of financial aid?
CSS has nothing to do with admissions.
Certainly incorrect CSS form or info will affect your financial aid award. There may be still time to send correct form/info.
In our experience, if any portion of the application is missing or incomplete, including financial aid, the college sends a message with the problem. I agree that your rejections wouldn’t have to do with making a mistake on the CSS profile. And I’m trying to remember, did the CSS profile have a different year options? But again just contact them and ask them how to submit a corrected CSS profile.