See it would be better if your medical officer have provided your chest measurement in inches then you should have ask him to write it in cm rather than doing it yourself. Although, there won't be any problem at all in the JOSAA Counselling but laterwards if you get such problems then I would recommend you to go for the issuing officer to change it.

In conclusion, you will not find any problem for JOSAA counselling.

To know more about the JOSAA counselling visit the link below:

https://engineering.careers360.com/articles/josaa

I hope this answer helps. All the very best for your future endeavors!