Assuming you have water without contaminants to affect the phase change temperatures (like sodium chloride), and also assuming you're at sea level (easily compensated by charts), then distiller water freezes at 32.000000000... F and boils at 212.0000000... F. Barometric pressure matters, but not enough to measure on your thermometer.

Getting a good slurry of crushed ice/water at equilibrium is important. You cannot have local hot spots.

These are know as physical constants, and are accepted in the metrology world as ultimate standards so long as you set up you baths correctly. In other words, they are not considered to be traceable to national standards, but are rather fixed to natural physical constants. Or, as one guy I used to work with said "traceable to God."

Now, do you have your bath at equilibrium? I don't know. Do you have a good slurry, or is your crushed ice in chunks that are too big? Technically it's supposed to be shaved ice, but for a home lab crushed is good enough.

Are you near sea level? Do you have the thermometers inserted into the fluid to the immersion line?