Question 547541
I assumed that the matrix you are talking about is
A={{{(
 matrix( 3, 3, 
   3,-2,-3,2,-1,0,2,3,-1)
)}}}
One way of finding the inverse is {{{A^-1=adj(A)/det(A)}}}, which involves calculating the determinant {{{det(A)}}} and the matrix {{{adj(A)}}}.
Calculating {{{det(A)}}} is complicated and you may make mistakes.
Calculating the matrix {{{adj(A)}}} is much worse.
I calculated det(A)=-25 and
{{{adj(A)=(
 matrix( 3, 3, 
   1,-11,-3,2,3,-6,8,-13,1)
)}}}
Amazingly, it checks. (I usually make mistakes in complicated calculations).
I cannot figure out where you could have made a mistake. Not enough information. I do not even know if your matrix is the same one I used. The inverse you calculated has 4 as denominator everywhere, so I imagine that you calculated the determinant of your matrix as 4.
If you search the internet for matrix inverse, you will find plenty of online explanations and instructions. There are online matrix calculators too, that will give you determinants, inverses, and more. Maybe you can use those to help yourself. It is likely to work better than trying to diagnose your problem through questions in this website.