ill tell ya how it is with double degrees
double degrees basically have more job prospects, so in your case doin commerce/science, means you can work in either fields, highly unlikely you work in both at same time, but if you got sick of science, you work in commerce or vice versa, at the end of the day its like you got 2 degrees in 1, which took u less time to complete.
but at the end, you will most likely only work in one field of study, but if you dont like working in science, which could be researcher...which is crap salary, or even science teacher i think.
commerce is where all the job prospects are, and its most likely you will be sticking to it in terms of career path, unless ofcourse money or job prospects dont concern u too much? lol
well thats my insight, everyones opinion is different hehehe.
but regardless, good for you on your choice