This Gemara is perfectly understood according to the Chalukat Hamishnayot as they are in the Mishnayot:
a) ... Konam sheAni yashen ... Shevua sheAni yashen ...
b) Korban lo Ochal lach ... Shevua lo ochal lach ...
The Chaluka of these Minshnayot in the Gemara however, is different. My question is who made the separation of the Mishnayot in the Gemara, were they Ravena and Rav Ashe or the Madpissim?
The answer is somewhere between the two. The old manuscripts of the Shas have all the Mishnayos together followed by all the Gemara. This arrangement has remained in the Vilna Shas (which we use today) in the ninth Perek of Berachos, the eighth Perek of Shavuos, and others.
However, it was the Rishonim who separated them, but not always in agreement. For this reason we find often that Rashi (or in Nedarim, the Ran) on the Mishnah appears later in the Gemara (sometimes even without that part of the Mishnah being mentioned). This is explained by the fact that Rashi had a different division of Mishnayos.