You are only at the begining of flower so your humidity could do with being a little higher but it's not the end of the world. The bigger your plants get the more they will transpire.
Underwatering your plants can cause low humidity. Make sure they are getting enough water. You should be fully saturating your pots each time you feed. Then feeding again when the weight of the pot is roughly half of that from the saturated weight. If they dry out more then your underfeeding and adding to your low humidity problems.
One budget tip without having to buy a humidifier is to have a bucket of water in your room, and have a towel half in and half out of the bucket, acting as a wick. Standing water does't evaporate very well at all, the towel aids this action. Maybe have a fan blowing over the towel too.
Good luck bro, it looks great so far!