PREVIOUS SINS will be PUNISHED if you continue doing AFTER Islam (after Allah guided you, after you became mindful about Allah)

Narrated Ibn Mas`ud: A man said, “O Allah’s Messenger (ﷺ)!

“Shall we be punished for what we did in the Prelslamic Period of ignorance?”

The Prophet (ﷺ) said,

“Whoever does good in Islam will not be punished for what he did in the Pre-lslamic Period of ignorance and whoever does evil in Islam will be punished for his former and later (bad deeds).

Sahih Bukhari
Reference: Sahih al-Bukhari 6921 (Apostates)
In-book reference:Book 88, Hadith 4