```javascript
// Google Apps Script to save form data to Google Sheet
// Deploy as a web app with these permissions:
// Execute as: Me
// Who has access: Anyone

const SHEET_ID = '12_0SbhoTQmgXFRLhyxXDoKxQNnvYGaVCc-Glmyqzbc0';
const SHEET_NAME = 'FormSubmissions';  // change if your sheet tab name is different


function doPost(e) {
  try {
    const data = e.parameter;
    const sheet = SpreadsheetApp.openById(SHEET_ID).getSheetByName(SHEET_NAME);
    
    // Get headers if sheet is empty
    const headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0];
    let nextRow;
    
    if (headers.length === 0 || headers[0] === '') {
      // First time setup - create headers
      const newHeaders = ['Timestamp', 'Name', 'Email', 'Phone', 'Country'];
      sheet.getRange(1, 1, 1, newHeaders.length).setValues([newHeaders]);
      nextRow = 2;
    } else {
      nextRow = sheet.getLastRow() + 1;
    }
    
    // Prepare data row
    const timestamp = new Date();
    const rowData = [
      timestamp,
      data.name,
      data.email,
      data.phone,
      data.interest
    ];
    
    // Add data to sheet
    sheet.getRange(nextRow, 1, 1, rowData.length).setValues([rowData]);
    
    // Return success response
    return ContentService.createTextOutput(
      JSON.stringify({result: 'success', row: nextRow})
    ).setMimeType(ContentService.MimeType.JSON);
    
  } catch (error) {
    // Return error response
    return ContentService.createTextOutput(
      JSON.stringify({result: 'error', error: error.toString()})
    ).setMimeType(ContentService.MimeType.JSON);
  }
}
```

To implement this:

1. Create a new Google Sheet and note its ID from the URL
2. Create a new Google Apps Script (Extensions > Apps Script)
3. Paste the google-script.js code and replace SHEET_ID with your actual sheet ID
4. Deploy the script as a web app (Publish > Deploy as web app)
5. Copy the web app URL and replace YOUR_GOOGLE_SCRIPT_ID in the index.html form script
6. The form will now submit data to your Google Sheet when submitted

The form includes:
- Loading state during submission
- Success/error messages
- Form reset on success
- Basic validation through required fields