A quantum Monte Carlo approach, considering all the corrugation effects, was used to calculate the complete phase diagram of the second 3He layer adsorbed on graphite. We found that a first-layer triangular solid was in equilibrium with a gas in the second layer. At a surface density 0.166±0.001Å-2, this fluid changes into two first-layer registered phases: 4/7 and 7/12 solids. The 7/12 arrangement transforms into an incommensurate triangular structure of ¿=0.189±0.001Å-2 upon further helium loading. A recently proposed hexatic phase was found to be unstable with respect to those commensurate solids.