The watts is the power rating of the resistor.
It is OK to have it too high, but bad to have it too low.
Unless you are working with power circuitry, or heavy loads, then it's pointless going for anything over 0.25W.
The actual power is defined by VI, or RI², or V²/R.
At 5V a 100? resistor would dissipate 5²/100 = (5*5)/100 = 25/100 = 0.25W.
A bigger resistance dissipates less power, a smaller one more power.
The power rating won't "stop" a resistor from working. If the power rating is too low, the resistor will get too hot, and in the worst case, catch fire.
Either the resistors you were sold were the wrong resistance, or you asked for the wrong resistance, or you have wired them up wrong.