Values from `.tfvars` not getting loaded

Question

I am new to terraform and building my first terraform script to launch instances in GCP. Values from terraform.tfvars are not being loaded and only default values from variables.tf are being loaded. Below are the commands that I am using to run to run the script. Can someone let me know the mistake I am doing?

terraform plan -var-file=terraform.tfvars
terraform apply-var-file=terraform.tfvars 

Below is the file structure

├── gcp_instance
│   ├── gcp_instance.tf
│   └── variables.tf
├── main.tf
└── terraform.tfvars

My main.tf file

module gcpinstance {
  source = "./gcp_instance"
} 

my gcp_instance.tf file

terraform {
  required_providers {
    google = {
      source = "hashicorp/google"
      version = "3.5.0"
    }
  }
}

provider "google" {
  region      = "${var.gcp_region}"
  project     = "${var.gcp_project}"
  zone        = "${var.gcp_zone}"
  credentials = "${var.gcp_credentials}"
}

resource "google_compute_instance" "vm_instance" {
  count        = length(var.instance_name)
  name         = var.instance_name[count.index]
  machine_type = element(var.instance_type, count.index)

  boot_disk {
    initialize_params {
      image =  element(var.instance_image, count.index)
    }
  }

  network_interface {
    network = "${var.gcp_network}"
  }
}

my variables.tf file

variable "gcp_project" {
  description = "Google Cloud Platform project"
  default     = "test"
}

variable "gcp_region" {
  description = "Google Cloud Platform's selected region"
  default     = "us-central1"
}

variable "gcp_zone" {
  description = "Google Cloud Platform's selected Zone"
  default     = "us-central1-f"
}

variable "gcp_credentials" {
  description = "Credential file to be used for this project"
  default     = "test"
}

variable "instance_tags" {
  type = list
  default = ["application1", "application2"]
}

variable "instance_type" {
  type = list
  default = ["f1-micro","f1-micro"]
}

variable "instance_name" {
  type = list(string)
  default = ["application1", "application2"]
}

variable "instance_image" {
  type = list
  default = ["debian-cloud/debian-9","debian-cloud/debian-9"]
}

variable "gcp_network" {
  description = "Network to be used"
  default     = "default"
}

variable "gcp_network_global_cidr" {
  description = "CIDR for the Instances"
  default     = "10.0.0.0/24"
}

my terraform.tfvars file

gcp_project = "test"
gcp_region  = "us-central1"
gcp_zone    = "us-central1-f"

gcp_credentials = "test.json"
instance_tags = ["application1", "application2", "application3"]
instance_type = ["f1-micro", "f1-micro", "f1-micro"]
instance_name = ["application1", "application2", "application3"]
instance_image = ["debian-cloud/debian-9", "debian-cloud/debian-9", "debian-cloud/debian-9"]

gcp_network = "default"
gcp_network_global_cidr = "10.0.0.0/24"