Tetanus shot 3/9 due to 2nd degree burn. Today I feel three hard bumps all together & a little tender. Should it feel like bumps on injection site?

It happens. It is not unusual for there to be a slight local reaction like you describe, with a little bit of swelling in the tissues under the skin (that's called induration in doctor talk). Tenderness also common for a couple of days. Can try cool compress on area, gentle massage, but take it as a sign that your body is mounting an appropriate response to the vaccine.
Shot reaction. As long as you do not have a fever which just started this is a normal reaction to the tetanus shot.