Sometimes to be able to hit harder and issue power suddenly its best not to try harder.
Instead, you should just relax and mentally detach yourself from the situation so that you will not mentally tense up.
After this, take a moment to mentally command yourself to remove excessive strength from your hands before you do the technique. Thereafter, you should be able to whip the power out a lot more stronger. With practice you should be able to do this quickly.
And be aware of obstacles to avoid unnecessary accidents when issuing force on your training partner.