I have heard the kaplan does purposely score you low on diagnostic tests to convince u that they helped u improve. Sometimes % can mean percentile instead of %correct
mock standardized score...
Look at what it says exactly. Did you get a score of 19 on the section, or did you get 19 correct out of 30 questions? Is the 45% the number of questions you got right, or Kaplan's estimate of your percentile?
I believe they are totally different concept. A percentile like yours mean under 45% of people score 19 or less. Your calculation is actually convertion of raw score. check out the sample exam on ADA and they have convertion table. Your score of 63% will be 17 or 18 on DAT score.