Select Non Contiguous dynamic range

I am trying to select a range that is dynamically generated where the rows and columns are not equal in length and there culd be empty cells.
I know the top left cell and need to select all cells included, so basically the max column and max row.

The sample.xlsm contains dynamically generated data. The top left cell of the range I would like to select is C3. In this example I would like to select the range C3:O16

Thanks for your help!
Sorry but not able to get this to work.
Firstly why B3 if my top left cell is C3?
I want to place a single line border around this selection