Cube Travel GTS SL size 58 fitting problems

I've got my hands on a used CUBE size 58. I'm 193 and I thought that would fit me. It doesn't, really. I'm now kinda stuck with this beautiful and technically speaking wonderful piece of engineering but... I feel my hands are loaded and it's not a position I can hold for longer than one hour. I feel like a bear on a tricycle. I'm extremely outta shape. I restarted cycling with my father's Legnano 2/3 months ago, a humble city bike and.. I started losing weight. I was 131kg, now I'm 123. I went and made myself a gift, but... I don't feel comfortable with it. Is it the size? I have a 58. I bought a riser but it's not really making a difference. It's just that I have to get used to the position and maybe fitter?

The Legnano was a damn armchair compared to this German stool! Please advise