led string getting very hot

Hello Saber people!

I saw a video on youtube by Space Windu with a cool white LED string in a blue blade, and i want something like that.
I could not find these 360° leds he is using. So i tried different white leds and made strings of 10 to compare them.
The best and brightest result I got from so called "diffused" leds.

I am having a problem to find the right resistor for this build. For now i just made a string of 30 leds. But they ae getting very hot, they melt the diffusion foam. btw, this happened with all types of leds i tryed.

I got me a nano biscotte v4 for this build but did not use i yet.
as powersupply i have a samsung 18650 2600mah.
the specifications of the leds are 2,8-3,6 v , 20-30 mA (somewhere it sais 25...?)
The battery gives fully charged 4,2 v. the nominal voltage is 3,7.

I don't know what the correct number are to calculate the right resistor.
with 4,2v battery, 3,6v led and 2000ma (assuming i will use 100 leds) i calculated a resistor with 0,3 ohm and 7.2 watts

i got me a resistor with 0.1 ohms but only 5 watts. i did use 3 in a row. But the leds are still getting very hot.
what am i doing wrong here?
please help.

You pretty much explained it.

Your resistance is too low, as is the wattage.

Go up to 8 or 10 watt.Or split the string into sections.