Hi, i also studied only K&B and just gave three or four mocks in which my score ranged from 50% -75%..but i cleared the SCJP 6 exam last week with 91%, so my point is your preparation level is alright. I think whats important for the exam is confidence, which can only be achieve through practice. I wrote a lot of small codes to get my concepts rights. So make sure, you practice well.
And dont worry you can crack the exam buddy..trust yourself! Best of luck