The crystal structure shows a strangely distorted molecule with only $C_\mathrm{i}$ symmetry. Values have quite a wide range, $\angle(\ce{CCH})\approx 100-120^\circ$. See below for all values and xyz coordinates to read in with a molecular viewer. Source:
R. Kahn, R. Fourme, D. André and M. Renaud, Acta Cryst. 1973, B29, 131-138.
A DF-BP86/def2-TZVPP calculation (gas phase, 0 K) gives a highl $D_\mathrm{3d}$ symmetric structure with
\begin{array}{ll}
\angle(\ce{CCH_{ax}}) & =109.1^\circ,\\
\angle(\ce{CCH_{eq}}) & =110.3^\circ,\\
\angle(\ce{CCC}) &=111.5^\circ,\\
\angle(\ce{H_{eq}CH_{ax}}) &=106.4^\circ.\\
\end{array}
Also Bond length differ very slightly (and impossibly to determine at room temperature and pressure), with
\begin{array}{ll}
\mathbf{d}(\ce{CC}) &=1.537~\mathrm{\mathring{A}},\\
\mathbf{d}(\ce{CH_{ax}}) &=1.105~\mathrm{\mathring{A}},\\
\mathbf{d}(\ce{CH_{eq}}) &=1.103~\mathrm{\mathring{A}}.\\
\end{array}
The tiny differences can be explained with Bent's rule.
In principle the assignment Goeff already gave you is absolutely valid, especially if you take the dynamic nature of the molecules into account that they have at standard temperature and pressure.
Also see xyz coordinates for visualisation below.
Appendix
Crystal structure
\begin{array}{lr}
R(1-2) &1.528 \\
R(1-3) &1.519 \\
R(1-4) &0.884 \\
R(1-5) &1.146 \\
R(2-6) &1.055 \\
R(2-7) &0.929 \\
R(2-10) &1.521 \\
R(3-8) &1.100 \\
R(3-9) &0.944 \\
R(3-11) &1.521 \\
R(10-12) &1.519 \\
R(10-13) &1.100 \\
R(10-14) &0.944 \\
R(11-12) &1.528 \\
R(11-15) &1.055 \\
R(11-16) &0.929 \\
R(12-17) &0.884 \\
R(12-18) &1.146 \\
A(2-1-3) &110.4 \\
A(2-1-4) &106.7 \\
A(2-5) &105.8 \\
A(1-2-6) &106.6 \\
A(1-2-7) &118.2 \\
A(1-2-10) &111.3 \\
A(3-1-4) &103.0 \\
A(3-1-5) &114.0 \\
A(1-3-8) &110.6 \\
A(1-3-9) &116.9 \\
A(1-3-11) &112.4 \\
A(4-1-5) &116.7 \\
A(6-2-7) &109.5 \\
A(6-2-10) &110.6 \\
A(7-2-10) &100.5 \\
A(2-10-12) &112.4 \\
A(2-10-13) &109.1 \\
A(2-10-14) &100.4 \\
A(8-3-9) &106.9 \\
A(8-3-11) &109.1 \\
A(9-3-11) &100.4 \\
A(3-11-12) &111.3 \\
A(3-11-15) &110.6 \\
A(3-11-16) &100.5 \\
A(12-10-13) &110.6 \\
A(12-10-14) &116.9 \\
A(10-12-11) &110.4 \\
A(10-12-17) &103.0 \\
A(10-12-18) &114.0 \\
A(13-10-14) &106.9 \\
A(12-11-15) &106.6 \\
A(12-11-16) &118.2 \\
A(11-12-17) &106.7 \\
A(11-12-18) &105.8 \\
A(15-11-16) &109.5 \\
A(17-12-18) &116.7 \\
\end{array}
C 2.329589000 3.011988000 -0.044238000
C 3.630888000 2.632672000 0.661249000
C 1.367908000 1.836044000 -0.049671000
H 2.524936000 3.113740000 -0.900292000
H 1.933922000 3.936128000 0.506802000
H 3.388552000 2.469096000 1.674854000
H 4.348450000 3.220000000 0.605369000
H 1.030575000 1.607424000 0.972471000
H 0.592407000 1.921052000 -0.581309000
C 4.247092000 1.383956000 0.049671000
C 1.984112000 0.587328000 -0.661249000
C 3.285411000 0.208012000 0.044238000
H 4.584425000 1.612576000 -0.972471000
H 5.022593000 1.298948000 0.581309000
H 2.226448000 0.750904000 -1.674854000
H 1.266550000 -0.000000000 -0.605369000
H 3.090064000 0.106260000 0.900292000
H 3.681078000 -0.716128000 -0.506802000
Computed (DF-BP86/def2-TZVPP)
C -1.270112000 -0.733300000 0.229506000
C 0.000000000 -1.466599000 -0.229506000
C -1.270112000 0.733300000 -0.229506000
H -1.328386000 -0.766944000 1.332131000
H -2.167276000 -1.251277000 -0.145050000
H 0.000000000 -1.533888000 -1.332131000
H 0.000000000 -2.502555000 0.145050000
H -1.328386000 0.766944000 -1.332131000
H -2.167276000 1.251277000 0.145050000
C 1.270112000 -0.733300000 0.229506000
C 0.000000000 1.466599000 0.229506000
C 1.270112000 0.733300000 -0.229506000
H 1.328386000 -0.766944000 1.332131000
H 2.167276000 -1.251277000 -0.145050000
H 0.000000000 1.533888000 1.332131000
H 0.000000000 2.502555000 -0.145050000
H 1.328386000 0.766944000 -1.332131000
H 2.167276000 1.251277000 0.145050000