The Gemara in Shabbas 12b writes as follows
אָמַר רַבִּי יִשְׁמָעֵאל בֶּן אֱלִישָׁע: אֲנִי אֶקְרָא וְלֹא אַטֶּה. פַּעַם אַחַת קָרָא וּבִקֵּשׁ לְהַטּוֹת. אָמַר: כַּמָּה גְּדוֹלִים דִּבְרֵי חֲכָמִים שֶׁהָיוּ אוֹמְרִים לֹא יִקְרָא לְאוֹר הַנֵּר. רַבִּי נָתָן אוֹמֵר, קָרָא וְהִטָּה וְכָתַב עַל פִּנְקָסוֹ: אֲנִי יִשְׁמָעֵאל בֶּן אֱלִישָׁע, קָרִיתִי וְהִטֵּיתִי נֵר בְּשַׁבָּת, לִכְשֶׁיִּבָּנֶה בֵּית הַמִּקְדָּשׁ אָבִיא חַטָּאת שְׁמֵנָה Rabbi Yishmael ben Elisha said: I will read and will not adjust. Once he read a book by candlelight and sought to adjust. He said: How great are the words of the Sages, who would say that one may not read by candlelight. Rabbi Natan says: he read and adjusted, and he wrote in his notebook [pinkas]: I, Yishmael ben Elisha, read and adjusted a lamp on Shabbat. When the Temple will be rebuilt I will bring a fat sin-offering
The Rambam (Shegagot 15:1) explains that for any unintentional transgression for which a "Hedyot" (not a Nasi or Kohen Gadol) brings a Chatos (goat or sheep) a Kohen Gadol has to bring a Par (bull), with the condition that The Kohen Gadol was the one who ruled the ruling that led to the unintentional transgression. Otherwise, he is doesn't bring a Korban at all.
Being that Rabbi Yismael Ben Elisha was a Kohen Gadol (Berachos 7a), even if all the conditiona mentioned were met, he at most would have to bring a Par (bull). If so, why did he write "Chatas Shmeinah" in his notebook? The Lashon Nekeiva alludes to a regular chatos which has female animals and not the Par a Kohgen Gadol would have to bring.