No, it is not possible to have more sand than was originially present.
The yield of 105% shows that some errors had occurred during the course of the laboratory activity. There are many possible explanations for the extra product. For instance, it may be that the container on which the sand was put for weighing at the beginning of the laboratory activity is not the same one that was used to measure the final yield. Also, if the students did not allow the sand to dry very well before weighing, it will have more mass because of its water content.
