The offline answers you checked are likely wrong, nobody knows the correct answers of the NBME unless you do extended feedback.
In addition, the questions in NBME have different weight. Difficult questions have more weight than easy questions. Therefore, you cannot correlate between the number of correct answers and the three digit score.
Certainly, you don't need to answer 95% of questions correct to get 240 in NBME or in the real USMLE exam.