How is your other sensor working? Any problems?
Do Amazon have a no questions return policy in Britain as they do in the states? If so get an exchange or refund.
I'm assuming you didn't solved this problem, so here's my review:
So, I'm enrolled with this sensor, I did not buy it, but my boss, so now he wants me to use it, I find this forum and find it comes with no Data Sheet. I personally found
Sensata P4055 Pressure Transducer Datasheet which is not the same, but connections and wirings seem to be the same, and then I found the Amazon link Pressure Transducer Sender Sensor, 1/8NPT Thread Stainless Steel Pressure Transducer for Oil Fuel Air Water Pack of 2(100PSI): Amazon.com: Industrial & Scientific with a lot of information before the comments.
Actually it says that it's a linear output voltage, so that indicates there's no need to add a resistor or something to make the readings work.
Reading your code I see you stablished a range for the read pressures at 0 PSI and 100 PSI, and I'm thinking that might be your issue.
I'm going to try a code but for ESP32 which is at 3.3 V and see what happens, I think you also need to add the offset 0.5 at minimal and maximum.