  We construct isomorphisms between spaces of vector-valued modular forms for
the dual Weil representation and certain spaces of scalar-valued modular forms
in the case that the underlying finite quadratic module $A$ has order $p$ or
$2p$, where $p$ is an odd prime. The isomorphisms are given by twisted sums of
the components of vector-valued modular forms. Our results generalize work of
Bruinier and Bundschuh to the case that the components $F_{\gamma}$ of the
vector-valued modular form are antisymmetric in the sense that $F_{\gamma} =
-F_{-\gamma}$ for all $\gamma \in A$. As an application, we compute
restrictions of Doi-Naganuma lifts of odd weight to components of
Hirzebruch-Zagier curves.
