This internal contracting is normal. This chakra is the doorway for the Kundalini energy. Unless this is opened sufficiently, the energy cannot flow into the other chakras. I suggest you concentrate most of your time and energy into stimulating your Base chakra, at least in the early stages of chakra development. Many people, though, have reported to me strong energy and chakra sensation the first time they used them.
Some people have more natural chakra activity than others.
Lack of any sensation, though, will not stop you from stimulating and developing them, even if, as was my case, you feel nothing at first. I did not have ANY natural chakra activity or ANY natural psychic ability when I first started energy work. Stop And Check Check your muscles for any tensing during the energy raising and chakra stimulation exercises, and re-relax as needed. Your muscles will automatically try and respond to the mental action of pulling energy up through you. The sensations you will feel in your chakras can vary, according to the degree of activity occurring in them, i.e., your physical make up, natural ability, concentration and relaxation skills affect this.