I’m similar FB-UB as you. I have slim arms/shoulders. I did a size 8 D cup first time. It fits ok but I think I’ll do a 10 C cup with a bit of tinkering on the shoulders next time.
Hope this helps.
The piece you cut off is not used for the placket. There is a separate wider, longer pattern piece, number 16.
Hope you have worked it out or see this in time.
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