Programs that check written works for the presence of plagiarism do not have the function of preserving papers in the database, much less adding it to the site. And even if there is some strange plagiarism inspector which downloads students' work, loads them into the database and uploads it to the site, then it should take some time for the paper to be indexed. Until the paper is indexed it is not on the Internet. In order not to be afraid that such a thing can happen to your program, you need to use services that have a good reputation, such as service that you can find if you google "check my paper for plagiarism" and that is available by this link that helps students not only with checking papers for plagiarism, but also with writing whole papers without plagiarism. Use good services and everything will be fine.