if you recheck your traces, you may find shorts across LEDs in the schematic. You ought to be able to do this on 1 side. Show schematic and check. Put all your LED's in the same orientation perhaps vertically and try diagonal traces to resemble branches. Each IC needs a cap too. 0.1uF. (104) but version control of specs leave, a lot to be desired for date code, reason for change with no Rev B. change, which may cause interference on data integrity. (Notoriously bad specs for signal integrity specs on traces, heat spreading and logic level noise)
http://cdn.sparkfun.com/datasheets/BreakoutBoards/WS2812B.pdf