You must have your heat to high.
Here are the instructions I send to my customers:
RHINESTONE TRANSFER APPLICATION INSTRUCTIONS
* Preheat your iron to cotton setting (about 320-340 degrees).
* Place the transfer face down on a flat surface and careful lift the backing from the design. The rhinestones will stick to the clear plastic transfer sheet. If any if of the rhinestones have shifted during shipping carefully put them back into place using tweezers.
* Place the transfer, rhinestone side down onto your shirt and press down with your hand. If it is not in the centered or in the position you want it to be in just lift and reposition. (once you iron it onto the shirt you cannot adjust the rhinestones)
* Turn the shirt inside out. Place iron over the design area and apply steady pressure for 15 seconds. Please DO NOT move the iron around when applying heat as the rhinestones may shift. Place iron over another design area for another 15 seconds and repeat until the entire design is pressed. DO NOT overheat or glue will lose its adhesion.
* Set the shirt aside and allow it to cool for about 5 minutes.
* Turn the shirt to right side out. Slowly and carefully peel the clear plastic sheet away from the shirt. If any of the rhinestones lift with the plastic carefully place the plastic sheet back onto the shirt reapply heat again.
* Wash shirt inside out in cold water on delicate cycle. Hang or lay flat to dry.