Thank you all so much for your answers ^^. I was kind of freaking out that the temp of the substrate was too low but I'm now reassured; the temp at the bottom of my enclosure is 91F so so far so good ^^. Plus she has a ceramic cave with no bedding under (so that the ceramic bottom of the cave is directly above the heat-mat) the cave is thus at 88-90F it will be good for her.
Cheers everyone
expect more of me here very soon , I have a lot of questions and I'm really trying to provide as good as I can for my girl ^^