does the amount of blood circulate in a body is same before and after amputation?
The kidney regulates the amount of blood being produced and removed from/recycled in the body. Even if somehow the body lost no blood when it lost the limb, the kidneys would remove the excess blood as it filters. 

I think the misconception in asking this question is that the body knows how much blood to produce for the body. Yet, that isn’t the case, it just regulates the amount based on different signals it gets from the blood. 

More info: https://www.ncbi.nlm.nih.gov/m/pubmed/17630596/