Ikhlas (Sincerity) is a cause of erasing sins, even the Most Major of them. Ikhlas (Sincerity) melts away a lifetime’s worth of sins.
Ikhlas (Sincerity) is our savior in the hereafter, when you will hear the announcement, Allah said on the Day of Judgment, this day the truthfulness of the truthful ones will be benefited by it. That is the day the people of Ikhlas (Sincerity) will shine.
Don’t give up. Ikhlas (Sincerity) isn’t about removing insincerity from your heart forever and eliminating it. It’s about managing it and realizing it’s an ongoing struggle. It’s a battle that in of itself is a sign of sincerity that you’re scared of it.