If on Rosh Chodesh in Mussaf one cannot remember whether he said Mekadesh Yisroel V’Hazmanin or Mekadesh Yisroel V’Roshei Chodoshim, what should he do?
If one doesn’t remember if he ended the bracha correctly or not, if he does remember saying the correct bracha, (in our case the mussaf text) then we assume that he continued saying it the way he should and he is fine.
However if he knows that he ended the bracha the wrong way then he would have to daven mussaf again. The most important part of and bracha is the ending and if it wasn’t said correctly it has to be said again.
O:CH 64-4. Our case should be similar to that case.
If he said the wrong ending – see Minchas Elazar 3-19, Eishei Yisroel 32 ftnt. 104, this is similar to saying “mekadesh Yisroel v’hazmanim on Rosh Hashana that he also isn’t as saying the bracha, and he has to daven again, see Machzik Bracha 582-5.