You don't need your garden to be symmetrical. Get something that will be a similar size. I'd consider a mountain laurel.

The other option is to trim the trees that are producing so much shade.

I would not raise the bed with blocks. It will not look more professional. In fact I’d remove the blocks which are there, increase the width of the bed and delineate it from the grass with a crisp, sharp cut slit edge. Remove all the junk ie hose, trellis etc. Fill the bed with repeated groups of perennials with a couple of shrubs, not straight lines of different coloured blobs. Prune the rose right down if you want to keep it. And don’t worry about symmetry.