Conversion from structure to byte array & object to byte arr

This problem regarding byte alignment in the structure

You first structure contains 2 double values (total size 16) & second structure contains 3 int (total size 12)

3rd structure contains the both structure, in this case system allocate the size of 32 bit because the default alignment of the type is the size of its largest element in the structure in your case double is max

To fix this use the [StructLayout(LayoutKind.Sequential, Pack = 1)] , above the structure , then structure allocate memory only based on the data type in structure.