Listen mate, simply put, go for an excess.
I'm using 25.00ml 0.1mol acid with excess Mg. to equal it, it should be 2.43 grams (i think, sorry, but i'm really tired). Go for an excess of say... 5 grams, then you shouldn't have much problem....
Let me know if i'm wrong, this is something that i'm not excellent at in all honesty.
pm me if you wanna discuss more... will try to be of help (Y)