Probably you miscalculated something. Using
QucsStudio "Transmission Line Calculator" 50 ohm 360 degree angle line length is 5.19mm, width is 1.23mm (on a 0.5mm er=3.38 substrate)
Using formulas lambda=C/(f*sqrt(er)):
lambda=299792458/((27*10^9)*Sqrt(3.38))*1000 'mm
lambda = 6.039467
lambda*0.1 ' 10% mm
Ans = 0.603947
It looks like around 0.6mm
I've checked some old designs:
FR4 amplifier + antenna X band: 1.0mm substrate, approximately 7% of wavelength in dielectric
F4B antenna K band: 0.5mm substrate, approximately 7% of wavelength in dielectric
If you plan to manufacture it, first make sure required height is available at PCB fab. In my experience for some substrate heights manufacturing price may be around 4 times higher, I try to avoid those.