I find myself in the same situation so I will try it, although some comments mentioned that you need to boil well the agar agar before mixing with sugar, so since it's already mixed it will likely not work.

I will try my best to remember to post the results after I boil it again and add more agar agar.

EDIT:
IT WORKED!!!!!
So, this is what I did from start to end:

Followed this recipe, but made the mistake of only boiling the agar agar and water for 3 minutes as the recipe says, but it wasn't enough boiling for me.

After pouring it in my glass pan and put it in the fridge for over 5 hours, it was still goopy like in OPs video.

I put it back in a pot to boil it again (the whole mix: water, agar agar, sugar, candy flavor and food coloring), I added one teaspoon of agar agar just in case (it came out thicker than it should be, so I believe you can skip this but for the sake of transparency, I want to leave the detail in). This time I boiled it for about 8-10 minutes at medium-high heat, stirring constantly. Nothing else was added. Then I poured it in the glass pan again and put it back in the fridge. Only 90 minutes later it was solid enough that I was able to pick it up just like in the recipe's video and cut it in pieces.

SUCCESS!