You should rather Daven two Maarivs.
In this case, you can’t (according to one shittah which we are choshesh for), because there is nothing being added, since the reason you need to daven again is for missing Yaaleh V’yavo, but you can’t say it now anyway since it is no longer Rosh Chodesh. Nor can you make it a tefillas nedavah b’tnai, because we don’t say tefillas nedavah on Shabbos.