Sketchup making me MAD!!!

[banditpowdercoat]

OK what am I doing wrong. I'm trying to make my tank in Sketchup, I have the bottom pane, and the back pane, but trying to make the front pane. I click one corner, then over to the other corner, click. Then go straight up fr height, but my mouse pad is not sensitive enough to just go to the height I want. I try type in 24, for 24" tall, and it makes the pane 24" long, with whatever height the mouse was at when I typed 24???? \

I did it for the back pane, whats going on here Grrrrr
Help before I go nuts