I have the tstat probe in the middle of the rack right in top of the heat tape and the thermometer probe i have it inside the tub where my hotspot is and i have both taped with black electrical tape
Make sure the tape is not covering the probe and is only holding the probe in place by securing the wire just behind the probe. Placing tape over the probe can trap heat and mess with your numbers.
also i have a another thermometer next to the tstat probe in the same place in the heat tape and its like 1.5 degree up then the tstat temp
Every thermometer will have a degree of error. This number is actually published in the details on most websites so this is normal.
im using the temp gun in top of the substrate cus the acurite probe is also in the top of the substrate
You should track the temps under the substrate on the bare tub floor. The probe laying on the substrate is not contacting fully to the heated area and is probably not getting heat properly to report correct numbers.
Remove all tape from inside the tub. Google Tape on Snakes to see the horrific damage it can cause to your snake. It is not pretty. Hot glue is usually a good choice as it is easy to use and easy to pull up. Just don't cover the probe, only secure the wire.