How do i send a response to the front end whether or not the if statement is true

How do i send a response to the front end whether or not the if statement is true
i tried to use res.status() but when i look at the response it has not changed
im recieving this response from the front end
Request URL: http://localhost:3000/register?
Request Method: GET
Status Code: 304 OK
even though im trying to get a response from the backend with either res.status(200)
or res.status(400)

const UserModel = require("./Server/models/User")
const Post = require("./Server/models/Post")
const mongoose = require("mongoose")
const bodyParser = require("body-parser")
const express = require("express")
const app = express()

mongoose.connect("mongodb://localhost:27017/BlogSite")




    



app.use(express.json())

app.get("/",(req,res)=> {
    res.send("Home")
})




app.post("/api/register",(req,res)=> {
  
    console.log(req.body)
    const username =(req.body.username)
    const password = (req.body.password)
 
    UserModel.create({username:username,password:password},(err) => {
        if (err) {
            console.log(err)
        }
        else{
            console.log("User Created")
            res.status(200).send("Home");
        }
    })
    

    
    
    
});

app.post("/api/login",(req,res)=> {
UserModel.find({username: req.body.username,password :req.body.password},(err,data) =>{
    

    if (data.length == 1){
        console.log("Logged in")
       app.post("/api/restatus",(req,res)=>{
           console.log("sent")
       })
    }
    else{
        console.log("Wrong Email or password")
        res.status(401)
    }
})
})



app.listen(3001,()=> {
    console.log("listening on port 3001")
})

Frontend

import React, { useState } from 'react';
import './App.css';

function Register() {
const [username,setUsername] = useState("")
const [password,setPassword] = useState("")


function handleSubmit(event) {
event.preventDefault
fetch("http://localhost:3001/api/register",{
  method:"post",
  headers:{
    "Content-Type" : "application/json"
  },
  body:JSON.stringify({username:username,password:password})
})
.then(function(res){ console.log(res) })
.catch(function(res){ console.log(res) })


} 



  return (
    <div className="App">
      <form onSubmit={handleSubmit}>

        <input placeholder="username" value={username} onChange={ e => setUsername(e.target.value)} />
        <input placeholder="password " value={password} onChange={ e => setPassword(e.target.value)}/>
        <button  type='submit' >Submit</button>
      </form>
    </div>
  );
}

export default Register;