XZ Gantry Question

I am just in the assembly phase of a newly purchased longmill ( very excited) I have just completed the XY gantry and notice that the two pieces seem slightly out of square with each other. The Front plate that mounts to the Router bracket and moves on the vertical access along the rails seems a bit out. I assume this can be adjusted otherwise the router would sit slightly out of plumb. I am sorry if I am jumping ahead Someone who is new to this type of equipment Just thought I should ask the question