Hi all i am completely new to this can,

Hi all i am completely new to this can, can some one please help me with my code. What i am trying to do is make my comet chase stop at the end of my LED strip (300) and then turn the whole strip yellow in a back wash effect to look like a explosion. I have spent way to long on this going round and round in circles. see code below

#include “FastLED.h”
#define LED_TYPE NEOPIXEL // Strip type: NEOPIXEL, APA102, LPD8806, etc.
#define DATA_PIN 6
#define NUM_LEDS 300
CRGB leds[NUM_LEDS];

int16_t positionDot1 = 2; // Set initial start position of pixels
int16_t positionDot2 = 3;
int16_t positionDot3 = 4;
int16_t positionDot4 = 5;
int16_t positionDot5 = 6;
int16_t positionDot6 = 7;
int16_t positionDot7 = 8;
int16_t positionDot8 = 9;
int16_t positionDot9 = 1;
int8_t delta = 1; // Using a negative value will move pixels backwards.
uint16_t holdTime = 100; /// speed

//---------------------------------------------------------------
void setup() {
Serial.begin(115200); // Allows serial monitor output (check your baud rate)
delay(3000); // Startup delay
FastLED.addLeds<LED_TYPE,DATA_PIN>(leds, NUM_LEDS);
}

//---------------------------------------------------------------
void loop() { // START MAIN LOOP

EVERY_N_MILLISECONDS(holdTime) {

// Set pixel color
leds[positionDot1] = CRGB(31,31,31);   /// set colors 
leds[positionDot2] = CRGB(69,69,69);
leds[positionDot3] = CRGB(100,100,80);
leds[positionDot4] = CRGB(131,131,120);
leds[positionDot5] = CRGB(162,162,100);
leds[positionDot6] = CRGB(193,193,50);
leds[positionDot7] = CRGB(224,224,25);
leds[positionDot8] = CRGB(255,255,0);
leds[positionDot9] = CRGB(2,2,2);

// Show the pixels
FastLED.show();
//delay(holdTime);  // Delay for a bit.

// Set pixels back to Black for the next loop around.
leds[positionDot1] = CRGB( 0, 0,0);
leds[positionDot2] = CRGB( 0, 0,0);
leds[positionDot3] = CRGB( 0, 0,0);
leds[positionDot4] = CRGB( 0, 0,0);
leds[positionDot5] = CRGB( 0, 0,0);
leds[positionDot6] = CRGB( 0, 0,0);
leds[positionDot7] = CRGB( 0, 0,0);
leds[positionDot8] = CRGB( 0, 0,0);
leds[positionDot9] = CRGB( 0, 0,0);

// Set new position, moving (forward or backward) by delta.
// NUM_LEDS is added to the position before doing the modulo
// to cover cases where delta is a negative value.
positionDot1 = (positionDot1 + delta + NUM_LEDS) % NUM_LEDS;
positionDot2 = (positionDot2 + delta + NUM_LEDS) % NUM_LEDS;
positionDot3 = (positionDot3 + delta + NUM_LEDS) % NUM_LEDS;
positionDot4 = (positionDot4 + delta + NUM_LEDS) % NUM_LEDS;
positionDot5 = (positionDot5 + delta + NUM_LEDS) % NUM_LEDS;
positionDot6 = (positionDot6 + delta + NUM_LEDS) % NUM_LEDS;
positionDot7 = (positionDot7 + delta + NUM_LEDS) % NUM_LEDS;
positionDot8 = (positionDot8 + delta + NUM_LEDS) % NUM_LEDS;
positionDot9 = (positionDot9 + delta + NUM_LEDS) % NUM_LEDS;
 }

}

Hello I do not see any test to stop the chasing you should have something like
if (positionDot9 <NUM_LEDS)

else {
Turn everything yellow
}

No ?