Sometimes I use organic top soil mixed with play sand
My eyes aren't spectacular anymore, so I may be wrong...but that looks to be 85 max? Basking spot should be between 95-105. Two suggestions, get RID of any sand, no matter the ratio. And pick up a Zoo Med digital thermometer, they are reasonable at 10 bucks and are sold online and in most pet stores. Far more accurate and reliable. The next step up would be what I call the heat gun...just point it and it tells you how hot a surface is.