The “expanded” (ie. doubled) version of speed 3 would be speed 1.5, which is of course impossible (*), so you must simply keep speed 3 and then double your bpm instead to 280bpm.
It is technically possible to achieve speed 1.5 by constantly alternating between speed 1 and speed 2, like so:
F101
F102
F101
F102
etc...
but… just save yourself the headache and used speed 3 @ 2x BPM