You guys must have missed something then. I use that recipe all the time and it works fine for me. If you undercook it, it will be gritty, but if you overcook it, it will harden into hard candy (not the best). I'll share my steps in the process, maybe it will help.
Step one
In a big pot, put a few inches of water and put on medium high to high heat. You want your water to just start boiling and then turn the heat down a little. In one bowl, mix your 3oz Jell-O with the 2.5 packets (0.25oz packets) unflavored gelatin. In another bowl put your 1/4 cup juice and 1 tablespoon honey and mix. To help mix the juice and honey, you can pop it in the microwave for 30 seconds, twice should be the most you'll have to do this. In a skillet (I use a 10" skillet, but you want something to fit on the pot) put your hash oil and then put the teaspoon of extract right on top. Stir together until dissolved well.
Step 2
Mix the juice and Jell-O together. Get a glass measuring cup and put hot water in and put it in the microwave for 3 minutes. This will keep the mixture warm longer while you pour it in the molds. Place your skillet on top of your pot and pour your Jell-O mix in. Stir well until the extract is mixed in and then stir occasionally throughout heating. I stir mine gently almost the entire time, but I don't think it's really necessary. This will usually take between 5-10 minutes, depending on how hot your water is. You want everything to be dissolved but don't let it get too hot.
​​​​​​Step 3
Take your measuring cup out of the microwave and dump the water out. Carefully pour the liquid from the skillet into the measuring cup, mixture will be hot as sh*t. Pour into molds and stick in refrigerator for an hour. You can leave them longer, it won't hurt anything. To preserve the gumminess, put in a ziplock bag and keep refrigerated.
Step 4 (optional)
I use this to keep the gummies from sticking together. In a baggie, pour some plain sugar. Take the gummies out of the molds and put them in with the sugar and shake. You can do one at a time or multiple, but it gets tricky with more. Take them out and put in a fresh ziplock bag and enjoy.
Hopefully this helps. Let me know if it changes your results.