What should a shofar do if an error is made during Rosh Hashanah blowing? Here is guidance from Rabbi Doniel Neustadt:
"There are basically two types of mistakes that the tokea can make while blowing shofar. The most common is that the tokea tries but fails to produce the proper sound. The general rule is that the tokea ignores the failed try, takes a breath, and tries again.(17)
"The other type of mistake is that the tokea blows the blast properly, but loses track and blows the wrong blast, e.g., instead of shevarim he thinks that a tekiah is in order, or instead of teruah he thinks that a shevarim is due. In that case, it is not sufficient to merely ignore the wrong blast; rather, the tokea must repeat the tekiah that begins this set of tekios.(18)
"When a tekiah needs to be repeated, it is proper that the makri notify the congregation (by banging on the bimah, etc.), so that the listeners do not lose track of which blasts are being blown."
17 Based on Mishnah Berurah 590:34, Aruch ha-Shulchan 590:20, and Da’as Torah 590:8.
18 Another example is when the tokea mistakenly blows [or begins to blow] two sets of shevarim or teruos in a row. The original tekiah must be repeated.