[Ethereum] Hardhat compile/deploy error

I'm following this tutorial for creating and deploying a smart contract (https://docs.alchemy.com/alchemy/tutorials/how-to-create-an-nft), but instead of deploying it on the ropstein test network I wanted to deploy it on the polygon mainnet.
The only change I made to the steps in the tutorial is changing the alchemy app from ropstein to polygon and using it's URL. The issue that i have is when I'm trying to compile the hardhat config file i get the output "Nothing to compile". Even if I try to run the deploy script I get the output "HardhatError: HH700: Artifact for contract "MyNFT" not found". I've tried different times remaking the project but i still get the same errors.

Smart contract file: MyNFT.sol

//Contract based on https://docs.openzeppelin.com/contracts/3.x/erc721

// SPDX-License-Identifier: MIT

pragma solidity ^0.7.3;


import "@openzeppelin/contracts/token/ERC721/ERC721.sol";

import "@openzeppelin/contracts/utils/Counters.sol";

import "@openzeppelin/contracts/access/Ownable.sol";

contract MyNFT is ERC721,  {

using Counters for Counters.Counter;

Counters.Counter private _tokenIds;

constructor() public ERC721("Metablooms", "MTBS") {}

function mintNFT(address recipient, string memory tokenURI)
    public 
    returns (uint256)
{
    _tokenIds.increment();

    uint256 newItemId = _tokenIds.current();
    _mint(recipient, newItemId);
    _setTokenURI(newItemId, tokenURI);

    return newItemId;
 }
}

Hardhat config file:

require('dotenv').config();
require("@nomiclabs/hardhat-ethers");

module.exports = {
    defaultNetwork: "matic",
    networks: {
        hardhat: {},
        matic: {
            url: "https://polygon-mainnet.g.alchemy.com/v2/...the rest of the url",
            accounts: ["my private key"]
        }
    },
    solidity: {
        version: "0.8.0",
        settings: {
            optimizer: {
                enabled: true,
                runs: 200
            }
        }
    },
    paths: {
        sources: "./contracts",
        tests: "./test",
        cache: "./cache",
        artifacts: "./artifacts"
    },
    mocha: {
        timeout: 20000
    }
}

Cmd output when I'm tryng to compile :

C:\Users\Filippo\my-nft>npx hardhat compile
Nothing to compile

Cmd output when I try to run deploy.js :

C:\Users\Filippo\my-nft>npx hardhat run scripts/deploy.js --network matic
HardhatError: HH700: Artifact for contract "MyNFT" not found.
at Artifacts._handleWrongArtifactForContractName (C:\Users\Filippo\my-nft\node_modules\hardhat\src\internal\artifacts.ts:478:11)
at Artifacts._getArtifactPathFromFiles (C:\Users\Filippo\my-nft\node_modules\hardhat\src\internal\artifacts.ts:592:19)
at Artifacts._getArtifactPath (C:\Users\Filippo\my-nft\node_modules\hardhat\src\internal\artifacts.ts:275:17)
at Artifacts.readArtifact (C:\Users\Filippo\my-nft\node_modules\hardhat\src\internal\artifacts.ts:58:26)
at getContractFactory (C:\Users\Filippo\my-nft\node_modules\@nomiclabs\hardhat-ethers\src\internal\helpers.ts:91:22)
at main (C:\Users\Filippo\my-nft\scripts\deploy.js:3:19)