Is there a Raspberry Pi B+ GPIO header footprint for kicad?
The Raspberry Pi B+ GPIO header is a standard 2x20 pin straight header.

The footprint for that part is the "Pin_Header_Straight_2x20" footprint in the "Pin_Headers" library that comes with with the current version of KiCAD.

The earlier Raspberry Pi B+ GPIO header is a standard 2x13 pin straight header.
The footprint for that part is the "Pin_Header_Straight_2x13" in the same "Pin_Headers" library.

All these parts have a 0.1" pitch -- in other words, the center of each pin is on a 0.1 inch (2.54 mm) grid.

Several inkjet printers are notorious for printing things with an X scale that is slightly off and a Y scale that is slightly worse.
You may find the KiCAD "Measurement_Scales" library useful in figuring out where things go wrong.
There's a pretty good chance that your Gerber files are actually perfect, and parts will fit perfectly on the boards made from those Gerbers, even if the parts don't seem to line up exactly perfectly on the rough-draft paper printouts from an inkjet printer.