You probably just need to add more batter! I fill my pans to about 3/4" from the top. It may dome a bit but I just cut off the dome and use scraps for cake balls or when it comes out of the oven I throw a tea towel over the top of it and gently press down all over the cake to help flatten it and no dome to cut off!
Amy
In the past I have mixed the batter just a little longer to get more air in the batter. I have also tried something my Wilton instructor told me "Add 2 Tbsp of meringue powder to your mix for added height."
Although both have worked for me, if I want real height I bake two 1/4 sheet cakes and stack them, with a filling in the middle.
Add more batter. You could also use the extender recipe if you just need a little more batter without adding a whole other mix.
I also fill my pans about 3/4 full (but on the larger ones or the 3" deep ones I use an inverted flower nail to help conduct the heat to the center for even baking).
I like the tall cakes, too. 
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