The objective of printing money is to respond to inflation, not to keep up with changes in GDP. If the inflation rate is high and the stock of money in the economy remains constant, the real amount of money will decrease as the value of money will decrease. ("Real" has a specific definition in economics that you should try to learn. It refers to the inherent value a good has, regardless of the nominal number of rupees that someone says the good is worth.) In studying economics, you will become aware that real fluctuations often matter much more than nominal fluctuations of economic variables. By that I mean that the inherent value of goods and services (what is actually produced) matters more than numbers that try to describe their value. Unfortunately, because of inflation, the numbers that we come up with about something like the stock of money do not give as much useful information compared to the real stock of money.
So, we are concerned about the real stock of money, and inflation erodes that, which is why more money must be printed in order for the real stock of money to be kept constant.
I have a personal aversion towards talking freely about "printing" money, because I think it obfuscates the much more nuanced and complicated process of money supply than simply asking a machine to print some notes. "Printing" money actually refers to money supply. The main component of that process is that the central bank buys bonds and other securities, thereby increasing the amount of liquidity in the financial market, and driving down interest rates. As interest rates go down, consumers and businesses have less incentive to save, so their consumption and expenditure will increase, along with an increase in demand for more liquid forms of money, one of which is physical currency.