Hi, I planted a fairly mature ( 8ft) clementine in my garden at my holiday home in Cyprus. It was planed about 8 months ago, it has a irrigation system so is water regularly and I feed it with fruit plant feed once a month. The tree has a good yield of fruit, however most are still green, that is behind the progress locally in the area where full orange fruits are being harvested, however the few fruits that have ripened on my tree to full yellow when opened are very dry, almost no juice.
I also think you might see an improvement in future years. If you just planted it 8 months ago the root system might not be well established yet. In my experience even mandarins that aren’t fully ripe can be very juicy, but not very sweet until they ripen further. Some of my mandarins produced dry fruit in their first years after planting. I’d give it another year and hopefully you get an improved crop next time.