How do I reduce the gap between flex MUI grids?

I am building a form using MUI. I have 6 fields and want to place them 3 of them on the left and the rest on the right, with a minimal gap. This is what I want to achieve:

This is what I have currently:

So far I have tried the gap property but no luck. I might be using the flex incorretly but again I’m not sure. This is the code I have:

import styled from "@emotion/styled";
import {
  Box,
  Button,
  Container,
  CssBaseline,
  Grid,
  Link,
  TextField,
  Typography,
} from "@mui/material";
import React, { useState } from "react";
const Field = styled(TextField)`
  // Custom TextField to avoid styling repetitions
  width: 650px;
`;
const FieldName = styled(Typography)`
  // Custom Typography to avoid styling repetitions
  font-weight: 700;
`;

const asterisk = <span style={{ color: "red" }}>*</span>;

const MailThread = () => {
  const [formData, setFormData] = useState({
    threadName: "",
    from: "Qmeter or 2354",
    customerName: "",
    subject: "",
    dropdownOption: "QNP-102 Template",
    to: [],
    startSending: new Date(),
  });

  const {
    threadName,
    from,
    customerName,
    subject,
    dropdownOption,
    to,
    starSending,
  } = formData;

  const onChange = (e) => {
    setFormData((prevState) => ({
      ...prevState,
      [e.target.name]: e.target.value,
    }));
  };

  const onSubmit = (e) => {
    e.preventDefault();
  };

  return (
    <Container maxWidth={false} component="main">
      <CssBaseline />
     
        <Box component="form" noValidate onSubmit={onSubmit} sx={{ mt: 3, display:'flex' }}>
          <Grid  container spacing={2}>
            <Grid item xs={12}>
              <FieldName>Thread Name{asterisk}</FieldName>
              <Field
                name="threadName"
                required
                value={threadName}
                onChange={onChange}
              />
            </Grid>

            <Grid item xs={12}>
              <FieldName>From</FieldName>
              <Field
                sx={{
                  backgroundColor: "#f8f4f4",
                }}
                disabled
                value={from}
                name="from"
                onChange={onChange}
              />
            </Grid>
            <Grid item xs={12}>
              <FieldName>If Customer name is empty</FieldName>
              <Field onChange={onChange} />
            </Grid>
            <Grid item xs={12}>
              <FieldName>Subject</FieldName>
              <Field placeholder="Enter subject here" onChange={onChange} />
            </Grid>
            <Grid item xs={12}></Grid>
          </Grid>
          <Grid container spacing={2} sx={{marginLeft:'10px'}}>
            <Grid item xs={12}>
              <FieldName>Template</FieldName>
              <Field placeholder="Enter subject here" onChange={onChange} />
            </Grid>
          </Grid>
        </Box>
      
    </Container>
  );
};

export default MailThread;