$1,000,000 is a lot for only 1 Bitcoin. Although Bitcoin started off worth almost nothing, and reached over $1000 at its peak in 2012, it is not likely that the price would go up to the hundreds of thousands, let alone the millions. Although, yes, there is a cap of 21M Bitcoins to be circulated, which would drive the price higher in the future, this is not a big enough factor to make 1BTC = $1M. Bitcoin being universally accepted by banks and businesses is likely to happen in the future, which would make demand high, which in turn would drive the price up. But again, this is not a big enough factor.
However, nobody can see far into the future. Anything can happen. Your investment in buying 21 Bitcoins may actually become $21M in the future. Who knows? As the poet Robert Frost once said in his poem The Road Not Taken: "And looked down one as far as I could/To where it bent in the undergrowth", he is trying to say that he can only see so far into the future, where the rest is a mystery. Have faith, and your dream might become a reality.
Good luck and we'll all be spamming you with messages of amazement when your prediction comes true.
