Thank you in advance!
Your numbers are right. You are just confused about matrix multiplication. See https://en.wikipedia.org/wiki/Matrix_multiplication (or any linear algebra textbook):
For matrix multiplication, the number of columns in the first matrix must be equal to the number of rows in the second matrix. The result matrix has the number of rows of the first and the number of columns of the second matrix.
If you really want a 5x5 matrix, you need to compute $U U^T$