Updating website glitches

I created my website some years ago and am now trying to update it by adding another section to my Portfolio.

I've added the section: Illustrations and Typography. However, it's not letting me design it as the other portfolio pages. These pages have galleries and work as a carousel. Now I only seem to be able to add sections so that it scrolls downwards. No options for gallery or carousel.

Is it to do with updates to the Squarespace interface or other? And if the gallery and carousel can work in the new interface, could you point me in the right direction?

Thanks so much.