Confused with network analysis
It's not clear to me the procedure you followed, but it seems to me you got it somewhat reversed.

Using obvious notations and calling \$V_{C1}\$ the voltage across C1:

\$V_o = V_{C1} \; \dfrac{R_L}{R_L+Z_{L2}}\$

where:

\$ V_{C1} = V_i \; \dfrac{Z_{eq}}{Z_{L1}+Z_{eq}} \qquad \$
and 
\$\qquad Z_{eq} = Z_{C1} \parallel (R_L+Z_{L2}) \$

put these equations together and you should have the solution.