Complete the missing pattern in the given $3\times 3$ shape matrix:

Let's count the number of sides for the shapes in each row and column:
* Triangle = $3$ sides
* Square = $4$ sides
* Pentagon = $5$ sides
* Hexagon = $6$ sides

Row 1: Triangle ($3$), Square ($4$), Pentagon ($5$)
Row 2: Square ($4$), Pentagon ($5$), Hexagon ($6$)
Row 3: Pentagon ($5$), Hexagon ($6$), $?$

The number of sides increases by $1$ as we move from left to right in each row. Following this pattern for the third row, the missing shape must have $6+1=7$ sides, which is a Heptagon.