Hello,
Hope you are doing well.
Many students while taking subjects in class 11 gets confused between maths and science, the only major difference between maths & science is that along with physics and chemistry you have to study maths in maths(PCM) and Biology in science(PCB)
The rest subjects are common between the two,also you can take an additional subject Maths with science if you wish to PCMB,If your goals is to go on Medical line then you can go for PCB or PCMB and if you want to get admission in an engineering college you should go for PCM.
Hope this was helpful to you.
All the best for a bright future!