how i can fix dimension of my different part of character

hello ; i am new in synfig ;
i made differents parts of my character ( head ,legs ,arms, body…) separately in differents canvas windows.
my problem is : when i put the different parts of my character in the same canvas windows , they don’t have the same dimension
for example the head is so big to the body or the legs are so small to the character …!!
how i can fix that??
please help me with clear steps because i am new user of synfig .

Please share here the file to be sure what are you talking about and guide on its fix.