You can only get the "Best Score!" trophy during the Epilogue (final chapter). It does not work in Chapter 4 when you play the Crash Bandicoot game for the first time. The reason is because you have an extra life in the Epilogue which gives you 500 bonus points. You must beat the high score of 3,500 points. With a few tries this should not be too difficult. You need to collect most of the apples and the extra life, do not die, and complete the level as quickly as possible. If you are short a few points, it is because you did not collect enough apples or missed the extra life from one of the boxes. The extra life is found in a wooden box relatively early in the level. If you do not collect the extra life, you cannot beat the high score.