Did you mean "in series"?
Every LED has a different forward voltage. Even LEDs made in the same factory batch have slight differences.
If you use one resistor, the led with the lowest forward voltage will receive the highest current. The led with the highest forward voltage will receive the lowest current.
So the LEDs will have slightly uneven brightness. This may not be noticeable.
LEDs do not last forever, although they can last many years or decades. The brightest led with the highest current will probably fail first.
When one LED fails, suddenly the other 2 LEDs will receive much more current. If this is above the maximum current they are rated for, they could fail very quickly. When the second led fails, all the current will go to the 3rd led which will not survive for long.
So, yes, damage could occur. But it depends on the value of the resistor and the current that flows, and the damage may not be noticeable for many years. How long do you think your project will last?
With 3 resistors, it may be many years before the first led fails. But when that happens, the other LEDs could last for several more years, instead of failing quickly afterwards. The other LEDs are not forced to share the current that the failed led would have received.
got it working in parallel as suggested. thank you paul,also @Wawa and @johnwasser for your advice.
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