When Rosh Chodesh is Friday, and is only one day, and you forget ya’aleh v’yovo at mincha, and you do not remember that you forgot until it is night, or until you have been mekabel Shabbos already, according to the Mishnah Berurah (though not the Aruch haShulchan, which only makes it more complicated) you CANNOT daven ma’ariv twice (meaning you cannot daven a ‘make-up’ tefillah at ma’ariv), since in such a case (forgetting YVY at minchah in a one-day Rosh Chodesh situation), MB holds you would have to make a tenaiy of ‘maybe-nedava’ at the ‘make-up’,and one cannot do that on Shabbos.
So please! Remember YVY at Minchah today!
The second day of Sivan, which this year is Shabbos, is traditionally known as Yom HaMeyuchos (loosely–the special day). Aruch haShulchan explains why: This is the day that Moshe Rabbeinu told B’nei Yisrael that they must sanctify themselves in preparation for mattan Torah. Sort of like what everyone will be doing iyh on Motzei Shabbos at out keness/Melava Malka, taking place in the Shul. We will primarily be hearing divrei hisorerus regading matan Torah, as well as secondarily be partaking at a seudas mitzvah (melava malka); thus, we are, as stated, doing it in the Shul.
See you there!