how to double my money in a few years without too much risk?

banks cant do that

Consider the "Rule of 72".

That is, divide 72 by a given rate of return or interest and the result is the number of years it will take you to double your money.

Example: 72 / 8 = 9 Meaning if a sum of money is getting a return of 8% it will take 9 years for that sum to double.

The problem these days is that low risk investments do not offer anywhere near 8%. The Ten Year Treasury bond is commonly known as the "risk free" investment. The 10 yr is currently yielding 3.83%. At that rate, it would take almost 19 years to double your money.