If i didn't experience any side effects from the first two moderna vaccine doses, am i likely to experience any from the booster shot?

most people symptoms after the booster are similar to symptoms after the 2nd of the 2 initial doses.....

May be mild. Your immune system should identify the booster as a target now, so may get some systemic effects--low grade temperature, aches, local soreness--for a couple of days. The Moderna booster is 1/2-dose, so this tends to minimize the likelihood and severity of any symptoms. Be well!