by fake you means creating copy of bitcoin or spending same coin more than once.
I bitcoin network once you send a transaction it takes some time to process, so suppose you send 2-3 transaction of 1 btc while your balance is just 1 btc only. Then any random node will process one and reject others. Similarly all other nodes will remove all those from their memory. So mathematically it is no possible to copy the transaction which we call as double spend.

Regarding supply, it has fixed supply and codes are publicly shown. So it is the currency which has no printer like native currency of many countries.