Guessing 2x9 means you have lost the granny. Adjust the "L" set screw so that the "middle" ring is as far as it goes. Set the shifter to the granny position or all cable released and connect it to the derailleur. Then shift to the middle position and adjust the "H" set screw so that it doesn't shift over the big ring.
Basically use the lower two positions on your shifter. That way it can't go slack on you.