Jelly & Pineapple Problem

I did that too, tried extra gelatine, but no success sadly

Pineapples have bromelain in them, which is an enzyme that breaks down proteins (it's sometimes called a 'flesh-eating' enzyme and it's what makes your tongue sting if you eat too much fresh pineapple). Gelatine is basically collagen, which is a protein, so that's why you can't put fresh pineapple in a gelatine-based jelly as the bromelain destroys the proteins so it'll never set. There's probably not a lot you can do now with the jelly beyond drinking it, bromelains are supposed to be anti-inflammatory so if you've got a cold it might help soothe your sinuses …

Potato flour added to hot cooked fruit will thicken it and give a clear jelly-like consistency, but I've never tried it with pineapple. (If you have potato flour, heat up your pineapple not-jelly in a saucepan, mix about 3 tbsp or half a cup of potato flour with a couple of spoonfuls of cold water to make a smooth paste, then add into your cooked fruit and keep stirring as it thickens. Then let it cool.) The joy of potato flour is that it becomes clear after cooking, unlike arrowroot which makes things cloudy.