This is normal for your meter. There will always be some residue capacitance.
Take the reading with the leads opened up. Then when taking a reading subtract the difference. The problem will be that even the physical position of the leads will change the readings a little.
For capacitors in the value range that you want to read, you really need a high end cap meter. Check out the higher end of the Fluke DVM's with the capacitor option. With these meters, you will have a much higher resolving and stability. But, when reading caps below 200 pF, you have to consider the wires. It is best to use very short wires something less than 4 inches with small clips in them.
For example, with a Fluke 89 series, they have excellent capacitance performance. There are also dedicated capacitor meters which are the best.
You can also set up a cap tester using a signal generator and a scope. If you want to do the math, you can work out a an RC network where you feed in a frequency and amplitude calibrated signal. You then use a dual trace scope and plot out the phase and amplitude differential. With some calculations you can then have a very precise reading of the cap.