Using deep and high-cadence gamma-ray burst (GRB) afterglow data from RATIR, we observe a sharp and achromatic light curve break 12.6 days after the GRB, accompanied by an approximately achromatic bump. Fitting of the optical, NIR, and X-ray data suggest a very narrow (2 degree) jet which remains collimated at late-time. We argue that the sharp light curve bump suggests an edge brightened jet, perhaps emitting only during a brief period of lateral jet expansion. The lightcurve also exhibits a

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... adual spectral evolution lasting >10 days. The evolution of the flux can be modeled as Flux∼(t/[20 days])^α(λ/[800 nm])^β, with a temporal slope α=-0.956 ± 0.003 and a gradually time-varying spectral slope β = (0.60 ± 0.07)+(0.26 ± 0.06) log(t/20 days).