Well made for a beta, but needs some tweaking
The only flaw I see is that the Ace should replace the 1 card. If possible, you should also have a way to only draw four of the same card, so as you draw, it becomes less likely to draw the same card. Also the more familiar name is "Blackjack". If you find a way to make two cards draw in the beginning and check if they are a Blackjack, that would also be cool.
Of course, like I said, for a start it's well done.