Your best bet is to rotate the yoke. Loosen the screws alongside it and carefully turn it (you'll have to do it while the monitor is on to see where you're turning it). DO NOT TOUCH THE SUCTION CUP-TYPE DEVICE (technically known as the anode cap) UNLESS YOU WANT A HUGE SHOCK!!! You'll need to be VERY CAREFUL while doing this.

I have done this on several compact Macs and often do it with a mirror in front of the display so I don't have to reach around the tube. Don't bother with the analog board unless this happens again over a very short time--in that case you may want to replace it, but as long as you get the yoke where you want it and tighten your screws properly you should be good to go with a non-tilted raster.