[JohnMitchel]

if i do the meditation very sincerily, may the bads inside me will automatically be erased or i have to strictly abide the five moral disciplines first?

Sila (morality) must come first. It precedes Samadhi in the Noble Eightfold Path, and the Suttas record Sila as being a necessary preparation for Samadhi in the gradual training.

That being said, one mistake is in thinking that one 'finishes' Sila before moving on to Samadhi - morality and meditation are recursive to one another, each of them doing their part to perfect ones initial Panna, and as such both ought to inform our practice.

If you break a precept, re-affirm your commitment to Sila by re-taking the precepts at the earliest opportunity. With this as a preparation, your meditation practice will be greatly improved.