Will this fit a 78cm long x 46cm wide change mat or would it be too big for it?

Hi Natalia, thank you for your inquiry, your change mat may not be big enough for this cover, however, your mat maybe deep so it may cover the extra space, do you have a local store you could possibly try this on? We hope this helps. if you follow the link https://www.babyonthemove.co.nz/store-locations/ this will take you to our online store finder. Here you can find contact details for your nearest Baby On The Move Store where one of our team experts will be happy to assist you in your product search and help answer any further questions you may have.