I think case, I would increase only the "outside" dimensions, so your end result is exactly what the pattern called for. How about this:
The 2 x 2 inch square cut 2 x 2 1/4. (Piece A)
The 2 x 3 1/2 inch rectangle don't change it. (Piece B)
The last piece 2 3/4 x 6 1/2 cut 3 x 7. (Piece C)
Sew the 2" side of A to B on each end. Then you should have a 7" piece that you can match to your C pieces.
But I'm with the poster above - if your blocks are coming out small, check your seam allowance and make it is smidge smaller.