Yes, in this case you may schedule immersion for Monday. Ordinarily, a
hefsek taharah should not be performed with toilet paper, primarily because it is difficult with toilet paper both to reach all crevices of the vaginal canal and to keep the paper from disintegrating at all. But, provided you did as thorough a
bedikah as possible, after the fact this can count as your
hefsek taharah.
For the future, we recommend buying a couple of extra packs of
bedikah cloths, one to leave in your purse and the other to leave somewhere in your office.