Hey @marceldc, the appearance of your slideshow on the link provided looks to be some WordPress auto formatting issues affecting the layout. I'll have a look into it, probably just a small bug I need to get fixed.
The customisation options you've mentioned aren't available at the moment but will be implemented again soon. It's already being worked on, but wasn't ready for the initial plugin release so it had to be held back temporarily. A visual interface for editing the slideshow styling is going to be added, very similar to the WordPress 'Customise' editor used to edit a themes styling visually. Until then, sorry about the inconvenience caused!
To center the slideshow, try putting it inside '<div align="center">' and '</div>'. This should do the trick. I'll make sure to add an option for this in the next update as well.