Can I apply for the entrance exam of LLM? I have scored 54.55% in LLB.

Yes, definitely! You can apply for LLM. There are some universities/colleges whose criteria is 50% or above. One such popular college is Amity University where LLM criteria is min 50% or above. Admission time is going on in various universities so stop wasting time & fill up the form till it ends.

No, you cannot. You need at least 60%.