How do I get rid of the feeling of wanting to return to sins after being guided, and will I be held accountable on the Day of Judgment for sins I was unaware of or did not realize their gravity?

You must strive to acquire beneficial knowledge so that you may recognize sins and discern their levels, thereby avoiding them. [Strive] also to comprehend their ugliness so you do not incline towards them, and to learn the levels of acts of obedience. Have a good opinion of Allah, repent to Him with sincere repentance, and persist in righteousness. Know that deeds are a means to attain Allah's mercy. Whenever your soul tempts you towards sins, remember their ugliness and harm. Seek help from the book "Al-Da' wa al-Dawa'" (The Disease and the Cure) by Ibn al-Qayyim, and associate with righteous people.