Siman 603
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א אַף מִי שֶׁאֵינוֹ נִזְהָר מִפַת שֶׁל עכוּ"ם, בַּעשֶׂרֶת יְמֵי תְּשׁוּבָה צָרִיךְ לִזָּהֵר. הַגָּה: וְיֵשׁ לְכָל אָדָם לְחַפֵּשׂ וּלְפַשְׁפֵּשׁ בְּמַעֲשָׂיו וְלָשׁוּב מֵהֶם בַּעֲשֶׂרֶת יְמֵי תְּשׁוּבָה; וּסְפֵק עֲבֵרָה צָרִיךְ יוֹתֵר תְּשׁוּבָה מֵעֲבֵרָה וַדַּאי, כִּי יוֹתֵר מִתְחָרֵט כְּשֶׁיּוֹדֵעַ שֶׁעָשָׂה מִשֶּׁאֵינוֹ יוֹדֵעַ, וְלָכֵן קָרְבַּן אָשָׁם תָּלוּי הֻצְרַךְ לִהְיוֹת יוֹתֵר בְּיֹקֶר מֵחַטָּאת (דִּבְרֵי עַצְמוֹ וְרַבֵּנוּ יוֹנָה רֵישׁ בְּרָכוֹת).
1 Even if one whom is not careful regarding non-Jewish bread [during the year], should be careful (during the ten days.) Rema: And there is to every person to search and inspect in their deeds and return from them in t'shuvah (repentance) during the (Ten) Days of T'shuvah. And a doubtful aveira (sin) needs more repentance from a certain aveira, because one that knows regrets more than one who does not know (which is the case when one is unsure). And therefore the Conditional Asham Offering needs to be more valuable than a Guilt Offering (Rema's own thoughts and Rabbeinu Yonah, beginning of Brachos).