Usually GMAT Prep is the single and only best indicator of your score.
However, you have to think if you encountered any repeat questions in your test - any questions that you have solved in the past. If yes, then your score is inflated. If no, then you are welcome to use the Q49/Q50 as your guidance. I do have to point out that our quant tests are quite accurate (questions are harder but the scoring algorithm has been honed to be within just 1-2 points of the actual test scores).
What I would suggest as the next steps is looking at your weaknesses and pursuing your mistakes. You don't need to take tests day in and day out but you do want to fix and patch the gaps you have. For that, a quiz would do better.
Good Luck!