how to increase file size in a memory module connected to arduino uno

Haii guys,
I am using a memory module with arduino uno to store some data.
I am simply creating a .txt file and writing some data to it and again reading all the data by reopening the file.

But I am facing a difficulty here, as I am unable to write all the data to one file. It seems that there is a limit of the size of the file. I can only enter half of the data in the file. For rest half i need to create one more file and store in it. But I want to write all of them in one single file.

I am using the simple code for storing data to memory card. Attaching the code also.

In the code below the whole data is not getting written to the file. If I am writing only 3 values, then it is getting stored.(NOT MORE THAN 3)

How should I do it?
Is there any way I can increase the size of the particular file?

Please HELP!!!

#include<SoftwareSerial.h>
#include <SPI.h>
#include <SD.h>
char reading[50]={0};
File myFile;
void setup() {
Serial.begin(9600);
 while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }
  Serial.print("Initializing SD card...");
  if (!SD.begin(4)) {
    Serial.println("initialization failed!");
    while (1);
  }
  Serial.println("initialization done.");
  // open the file. note that only one file can be open at a time,
  // so you have to close this one before opening another.
  myFile = SD.open("new2.txt", FILE_WRITE);
  // if the file opened okay, write to it:
  if (myFile) {
   reading = {23,34,avcdshweiw,ewruwuobbvbbvb,vcyusuffweowu8bcsdb,ssdgfdshfweh9,fdsjgfwieue,sdvfdsjdns};
    String data=reading;
    Serial.println(data);
      myFile.println(data);
    // close the file:
    myFile.close();
    Serial.println("done.");
  } else {
    // if the file didn't open, print an error:
    Serial.println("error opening new2.txt");
  }

  // re-open the file for reading:
  myFile = SD.open("new2.txt");
  if (myFile) {
    Serial.println("new2.txt:");

    // read from the file until there's nothing else in it:
    while (myFile.available()) {
      Serial.write(myFile.read());
    }
    // close the file:
    myFile.close();
  } else {
    // if the file didn't open, print an error:
    Serial.println("error opening new2.txt");
  }
}
    reading = {23, 34, avcdshweiw, ewruwuobbvbbvb, vcyusuffweowu8bcsdb, ssdgfdshfweh9, fdsjgfwieue, sdvfdsjdns};

What is this line supposed to do ?

Sorry for the confusion before. Actually problem is not the size of file. Problem is in the way i’m sending.
Now I am trying to figure out how to write data in sd card.

Now I am trying to figure out how to write data in sd card.

There are examples with the SD library