  Resonant dynamics plays a significant role in the past evolution and current
state of our outer Solar System. The population ratios and spatial distribution
of Neptune's resonant populations are direct clues to understanding the history
of our planetary system. The orbital structure of the objects in Neptune's 2:1
mean-motion resonance (\emph{twotinos}) has the potential to be a tracer of
planetary migration processes. Different migration processes produce distinct
architectures, recognizable by well-characterized surveys. However, previous
characterized surveys only discovered a few twotinos, making it impossible to
model the intrinsic twotino population. With a well-designed cadence and nearly
100\% tracking success, the Outer Solar System Origins Survey (OSSOS)
discovered 838 trans-Neptunian objects, of which 34 are securely twotinos with
well-constrained libration angles and amplitudes. We use the OSSOS twotinos and
the survey characterization parameters via the OSSOS Survey Simulator to
inspect the intrinsic population and orbital distributions of twotino. The
estimated twotino population, 4400$^{+1500}_{-1100}$ with $H_r<8.66$
(diameter$\sim$100km) at 95\% confidence, is consistent with the previous
low-precision estimate. We also constrain the width of the inclination
distribution to a relatively narrow value of $\sigma_i$=6$^\circ$$^{+1}_{-1}$,
and find the eccentricity distribution is consistent with a Gaussian centered
on $e_\mathrm{c}=0.275$ with a width $e_\mathrm{w}=0.06$. We find a
single-slope exponential luminosity function with $\alpha=0.6$ for the
twotinos. Finally, we for the first time meaningfully constrain the fraction of
symmetric twotinos, and the ratio of the leading asymmetric islands; both
fractions are in a range of 0.2--0.6. These measurements rule out certain
theoretical models of Neptune's migration history.
