In my opinion get rid of the calci-sand to start with, worst case scenario your beardie will start actively eating it for calcium boosts which is a one way road to impaction, mine is on cage carpet atm but also vinyl floor tiles and the like are good. Temperatures seem a little low for a youngster, basking spot should be around the 110F mark. If you have a 100w bulb you really want it on a dimming stat to keep control of the temps. If night time temps are low ideally you'd want a ceramic heat emitter on a stat. This will keep the temps from dropping too low but as it doesn't produce light it won't bother your beardie of a night time
I'm not 100% but I believe beardies can't feel heat from beneath them so the potential of burns from a heat mat is quite high as would be the respective vets bill.
Hope I've helped even a little bit