That's normal, since your tank is new and still in the cycling process. In fact, you want that to happen. Just keep up with the partial water changes, and eventually the nitrite readings will be replaced with nitrate, and your cycle will be done.
On another note, though, you should have added the cories after the cycle was done. You've overloaded your tank, and cories are sensitive to water conditions. Just keep an eye out for them and change your water partially each day. Don't add anything, because that will just mess your cycle up.