First, you'll have to change your Read Cell from a 2-D double to a 2-D string. There is now way you can get the word "End" out of a numeric array.
I would read the entire spreadsheet. Then Index out the first column and first row. Search each one for the word End. Now the index from the first column +1 is the number of rows you want. The index from the first row +1 is the number of columns. Use Array subset to get that part of the array using those two indices.