Two's Complement Multiplication

[Kimly]

How can I multiply signed numbers in two's complement form ??

I tried the ordinary way but it seems to work only if the product is the same size with the operators

for example :
4 * -4 = -16 ======> 0000 0100 * 1111 1100 = 1111 0000 works fine

but
50 * -50 = -2500 ======> 0011 0010 * 1100 1110 = 0010 1000 0011 1100
however it should be 1111 0110 0011 1100

How to Fix This ??