Thanks it works!
My code now is the following (hopefully it will help some other newbies like me)
x1_dataset = torch.tensor(D.inputFeature1.values, dtype=torch.float)

x2_dataset = torch.tensor(D.inputFeature2.values, dtype=torch.float)

x3_dataset = torch.tensor(D.inputFeature3.values, dtype=torch.float)

x_dataset = torch.stack([x1_dataset, x2_dataset, x3_dataset])