Temperature sensor (TMP36) inaccurate readings
Output voltage pec is 750mV @ 25'C nom and your reading is what from cold start to after a few minutes?   Does it change?
Spec is 1000 pF load max you are using twisted cable which is typically 5 pF/cm depending on tpi, diam. etc., so 50cm x 5 = 250 pF, so cable seems ok to prevent instability and oscillation. If you don't have a microamp analog meter get one or use series drop R to estimate.
Self heating from 5V should be less &lt; 0.05'C unless it is damaged so measure current against spec to ensure self-heating is not the issue. 
open air thermal time constant is &lt; 1 minute.. immersed in ice water is 3 seconds . what are the calibration results you get?
Do you have 0.1 µF cap across IC?
Did you add an op amp to compensate for offset only inherent to TP36 and not TMP35 or TMP37? VOUT @ 1mV/°F – 58°F  It is designed for 'F