@geleiap The slideshow height and width are missing in the slideshow dimensions. You need to set a slideshow height and width for the slideshows to work properly. The rest of the page is about 1000px width, you probably want the slideshow to be about 1000×288 pixels.
To get the best results, you should set the slideshow dimensions. Resize the slideshow images to the exact same dimensions in an image editor like Photoshop and then re-upload the resized images and set those images for the slide posts. If the sizes all match exactly it will fit together perfectly and if the slideshow is narrower than the width of the browser, it will be centered.
One more thing about your images, right now they are too large both in dimensions and file size. The first image is over 800KB, the whole homepage should be less than 1000KB to download. If you resize them all to the same correct size, and save them as JPGs, you should be able to get each image to be less than 100KB in size, greatly increasing the speed of your site.