Scratch cards do make some people millionaires, but whether they can make you one is something which it is not possible to answer.
Firstly you have to play scratch cards that have a prize of at least a million. Sometimes this is not easy as many have much smaller jackpot prizes than this. Then you have to play a great number of cards in order to increase your odds enough to give yourself a chance of winning. If you calculate the odds of winning the top prize, you will find that you have to spend the amount of the top prize, many times over just to give yourself a chance of winning the jackpot and so it is usually not worth doing.
Some people put winning down to luck and have the attitude that they are not lucky and never win. Luck does not exist and it is all down to giving yourself a good chance. The more times you play, the more chance you have of winning a big prize. Each ticket has the same chance of winning and there are lots of tickets which are not winning ones.
Basically, you can become a millionaire form a scratch card as long as you pick a card which has a prize of a million. However, the chances of winning that prize are very small and you are not very likely to win the prize. To calculate how likely you are to become a scratch card millionaire just find out how many people there are that have been made millionaires from scratch cards and how many scratch cards have been sold. You will find that many millions more scratch cards have been sold than there have been millionaires made.
There are probably better ways to become a millionaire than playing scratch cards but if you enjoy them, there is no harm in having a go. Just do not think that it easy to win a big prize, because it is not. It will not only be difficult, but almost impossible. Therefore just play for fun and see any prize as a bonus, never play with money that you cannot afford to lose and you will not only have more enjoyment form the scratch cards but you will not get yourself in to financial difficulty.