Turn 1, 6 and the last 2 turns (i.e. all the tight ones) it's best to shift down to 2nd on the entry and shortshift to 3rd as you begin to accelerate (Except for the final turn, you need to stay in second a little longer as it's tighter, so shortshifting too early will slow you down). For the second to last turn especially, I find it's extremely difficult to stay in 3rd, and you also need to brake a little earlier than you expect or you'll run wide.
Your lines are good. You're perhaps braking a little much for the second turn in the S-bend on the back of the circuit, but that may just be your driving style, i'm not sure if it has any effect of time (ordinarily I turn in early and coast into it but I might get on the power a fraction later, it's a trade-off)
The best advice I can give is to practice a lot. Sometimes that perfect lap just comes out of nowhere. I haven't found mine yet, i'm still hovering in the mid-1'32s because I keep making small mistakes, costing me precious tenths here and there.