Erik Kostson
Ansys Employee
If it works, I would say stick with it because membranes are very hard to get to work OK.

It looks like the folds want to straighten so that is going to be hard to do - try using stabilization (under and quasi static option (see below), and many substeps. These are all under analysis settings, and nonlinear controls (stabilization), and solver controls (Quasi-Static Solution -> Off or On) respectively.
If this does not work also, go to explicit LS-Dyna.
ALl the best