If you don’t need or cannot fit all eight sensors, the QTR-8x arrays can each be separated into two smaller sensor arrays that can function independently: a two-sensor array and a six-sensor array.
To break the board, use a sharp knife (e.g. hobby knife or box cutter) to score along the perforation (row of vias) between sensors 6 and 7. Place the long side of board on a flat surface with an edge, such as a table, so the perforation lines up with the edge. Hold the board against the table and press firmly down on the overhanging piece until it snaps off. If it doesn’t feel like the PC board is breaking, make the score deeper. You might want to file the broken edges of the boards.
Once the board is broken, you will need to modify the small piece slightly before it becomes functional. If you are operating at a Vcc of 5 V, solder the 100 Ohm through-hole resistor that was included with your QTR-8x across the two pins as shown below:
If you are operating at a Vcc of 3.3 V, short those two pins together with a piece of wire. With a connection in place between these two pins, the two-sensor board will function.
After the separation, sensor outputs 7 and 8 on the six-sensor board will no longer provide any signals.