I'm sorry man. Here's the deal. You can still use this. I would still recommend something else, but sometimes you have to deal with what you have. You will just have to be very careful. You said the cigars were at about 50% RH, right? First things first, pull that humidifier out of that plastic container at your very next opportunity. With luck you haven't had enough time to cause problems yet (no guarantees). Check the Humidity. If it's around 55%, close up the container (WITHOUT THE GEL PACK) and leave it sit. Monitor the humidity for a day or two. If it holds, great, if not put the gel pack back in until you get back up around 55% and pull it out. Wait until it holds that humidity for a day or two. At that point do the same thing up to about 60%. Rinse and repeat until you are where you want to be, then head over to either Heartfelt Industries, Cigarmony or HCM Cigar Beads and pick up a better humidification system. That last part is of course somewhat subjective and only a suggestion. If you are happy with 70% RH I'm sure that gel stuff will work OK for you.
All of the above assumes that your "plastic container" has a rock solid seal.