Remove the watermelon flesh, cutting with a serrated knife around the edges and scooping out
with a spoon. Transfer the flesh and pips into a food processor and blitz until smooth. Strain the pulp through a sieve or muslin cloth to extract all the juice(discard the pulp).

In pan take Agar agar in 1 cup of hot water and keep stirring till the agar agar dissolves in the water,Add sugar and stir it again till the sugar dissolves. If needed heat the mix over low flame to dissolve everything faster.
Strain the mix into a large mixing bowl to remove any undissolved particles (if any)

Add lemon juice to this and mix everything together. Taste and add more sugar if needed i.e if the watermelon is not sweet enough.
Pour the jelly mix into watermelon half.

Transfer to the fridge and allow to set for at least 8 hours, or preferably overnight. When u r ready to serve, use a serrated knife to cut the watermelon into wedges.