Looks good - congratulations!
How did you modify the plans to make her 18" - just increase the spacings between forms, or also increase the sections?
Only the length - form spacing and stems- were changed; the cross-sections stayed the same as designed.
From what I've seen, all of Bjorn Thomasson's plans come with a table showing several different overall length versions.
The Frej plans give mold spacings to build boats from 481 cm (15'9") to 533 cm (17'6") LOA.
I checked with Bjorn and he said that increasing the length up to 18' would be OK.
As the mold spacings get bigger, there's less support for the strips. So, with thinner strips, I had to be careful to keep things fair between the molds.
One important thing about changing lengths from plans - the cockpit position needs to be 'in the same place' - the same percent of the total length from the ends - to keep the boat balanced.