Yes. When opening an existing gallery, svBuilder-Pro has no knowledge of where your original images were stored when you initially added them to the project so it cannot resize them from scratch. (All svBuilder-Pro knows about are the originally-resized images in the 'images' folder.) You would need to delete the existing images in your gallery and re-add the images to be resized afresh.
Alternatively, you could resize your images first in an image manipulation program (such as Photoshop) and then choose for svBuilder-Pro to not resize them by deselecting the 'Resize Images' checkbox on the 'Images' tab.