Catbus game

I'm trying to make my cat only jump once until it lands back on the ground. I've tried to add a statement that makes it only go to a certain point, but the velocity keeps working against it. It begins to act like a basketball that has been bounced to much. I wouldn't want to add a collider (even though I have debated it). It would just make it worse...

The code is as follows:

let img; //background
var bgImg; //also the background
var x1 = 0;
var x2;

var scrollSpeed = 4; //how fast background is

let bing; //for music

let cat;

var mode; //determines whether the game has started

let gravity = 0.2; //jumping forces
let velocity = 0.1;
let upForce = 6;

let startY = 730; //where cat bus jumps from
let startX = 70;

var font1; //custom fonts
var font2;

p5.disableFriendlyErrors = true; //avoids errors

function preload() {
  bgImg = loadImage("backgwound.png"); //importing background

  bing = loadSound("catbus theme song.mp3"); //importing music

  font1 = loadFont("Big Font.TTF");

  font2 = loadFont("Smaller Font.ttf");
}

function setup() {
  createCanvas(1000, 1000); //canvas size

  img = loadImage("backgwound.png"); //background in

  x2 = width;

  bing.loop(); //loops the music

  cat = {
    //coordinates for catbus
    x: startX,
    y: startY,
  };

  catGif = createImg("catgif.gif"); //creates catbus
  catGif.position(cat.x, cat.y); //creates position
  catGif.size(270, 100); //creates how big

  mode = 0; //game start
  textSize(50); //text size
}

function draw() {
  let time = frameCount; //start background loop

  image(img, 0 - time, 0);

  image(bgImg, x1, 2, width, height);
  image(bgImg, x2, 2, width, height);

  x1 -= scrollSpeed;
  x2 -= scrollSpeed;

  if (x1 <= -width) {
    x1 = width;
  }
  if (x2 <= -width) {
    x2 = width;
  } //end background loop

  fill("white"); //text colour
  if (mode == 0) {
    textSize(20);
    textFont(font1);
    text("press SPACE to start the game!", 240, 500); //what text to type
  }

  if (mode == 0) {
    textSize(35);
    textFont(font2);
    text("CATBUS BIZZARE ADVENTURE", 90, 450); //what text to type
  }

  cat.y = cat.y + velocity; //code for jumping
  velocity = velocity + gravity;

  if (cat.y > startY) {
    velocity = 0;
    // cat.y = startY;
  }

  catGif.position(cat.x, cat.y);
}

function keyPressed() {
  if (keyCode === 32) {   //spacebar code
   // if ((cat.y = 730)) {
     // cat.y > 730;
      mode = 1;
      velocity += -upForce;
    }
 // }
}