Need the ID of the current row inserted within a transaction

Within a transaction I'm inserting a row.

How can I access and return the ID of the inserted row. As you can see in the code below(See under comment // Return last Inserted ID.) I tried to use the LastInsertedId() function, but it gives me an error back.

Btw, I'm using Postgres.

What am I missing here? Thx!

/**
 * Creates order and returns its ID.
 */
func createOrder(w http.ResponseWriter, r *http.Request) (orderID int) {

    // Begin.
    tx, err := db.Begin()
    if err != nil {
        log.Fatal(err)
    }

    // Db query.
    sqlQuery := `INSERT INTO ORDER_CUSTOMER
        (CUSTOMER_ID)
        VALUES ($1)
        RETURNING ID`

    // Prepare.
    stmt, err := tx.Prepare(sqlQuery)
    if err != nil {
        log.Fatal(err)
        return
    }

    // Defer Close.
    defer stmt.Close()

    customerEmail := validateSession(r)
    ID := getIDFromCustomer(customerEmail)
    order := order{}
    order.CustomerID = ID

    // Exec.
    ret, err := stmt.Exec(order.CustomerID)

    // Rollback.
    if err != nil {
        tx.Rollback()
        e := errors.New(err.Error())
        msg.Warning = e.Error()
        tpl.ExecuteTemplate(w, "menu.gohtml", msg)
        return
    }

    // Return last Inserted ID.
    lastID, err := ret.LastInsertId()
    if err != nil {
        orderID = 0
    } else {
        orderID = int(lastID)
    }

    // Commit.
    tx.Commit()

    return orderID
} // createOrder

Here is a working solution for now, further improvement is welcomed.

/**
 * Creates order and returns its ID.
 */
func createOrder(w http.ResponseWriter, r *http.Request) (orderID int) {

    // Begin.
    tx, err := db.Begin()
    if err != nil {
        log.Fatal(err)
    }

    // Db query.
    sqlQuery := `INSERT INTO ORDER_CUSTOMER
        (CUSTOMER_ID)
        VALUES ($1)
        RETURNING ID`

    // Prepare.
    stmt, err := tx.Prepare(sqlQuery)
    if err != nil {
        log.Fatal(err)
        return
    }

    // Defer Close.
    defer stmt.Close()

    customerEmail := validateSession(r)
    ID := getIDFromCustomer(customerEmail)
    order := order{}
    order.CustomerID = ID

    // Exec.
    _, err = stmt.Exec(order.CustomerID)

    // Rollback.
    if err != nil {
        tx.Rollback()
        e := errors.New(err.Error())
        msg.Warning = e.Error()
        tpl.ExecuteTemplate(w, "menu.gohtml", msg)
        return
    }

    // Return last Inserted ID.
    //lastID, err := ret.LastInsertId()
    err = stmt.QueryRow(order.CustomerID).Scan(&orderID)
    if err != nil {
        orderID = 0
    }

    // Commit.
    tx.Commit()

    return orderID
} // createOrder