the Mishna in Sanhedrin disagrees with you [that every Jew will merit Olam Habah]. It lists the people who don’t get a portion in Olam Habah.
This is a complex and lengthy topic that deserves its own thread.
But see this letter which proves this idea with many sources, and answers regarding the mishna Sanhedrin:
https://hebrewbooks.org/pdfpager.aspx?req=15875&st=&pgnum=174