could not find xlsx file path during running of program

Question

So, originally my program used a static spreadsheet named test, but to further enhance my program, I wanted it to make it to where the name within the textbox is the name of the file to use for the program; named: test.xlsx

So I believed I called the code properly here:

    public static string nameofexcelfile;
    public Form1()
    {
        InitializeComponent();
        nameofexcelfile = textBox4.Text + ".xlsx";
    }

    private void Form1_Load(object sender, EventArgs e)
    {
        OpenFile();

    }

    public void OpenFile()
    {

    
        //Excel excel = new Excel(@"Test.xlsx", 1);
        Excel excel = new Excel(nameofexcelfile, 1);
        textBox1.Text = excel.ReadCell(1, 0);
        textBox2.Text = excel.ReadCell(1, 1);
        textBox3.Text = excel.ReadCell(3, 2);
        
    }

Here is my Excel.cs class file:

    internal class Excel
    {

        string path = "";
        _Application excel = new _Excel.Application();
        Workbook wb;
        Worksheet ws;



        public Excel(string path, int Sheet)
        {
            //this.path = path;
            //wb = excel.Workbooks.Open(path);
            this.path = Form1.nameofexcelfile;
            wb = excel.Workbooks.Open(Form1.nameofexcelfile);
            ws = wb.Worksheets[Sheet];

        }

        public string ReadCell(int i, int j)
        {
            i++;
            j++;
            if (ws.Cells[i, j].Value2 != null)
                return ws.Cells[i, j].Value2;
            else
                return "";
        }
    }
}

Within my Excel.cs class; I named a string and gave it the default location "" as the Documents folder, and this was named:

string path = "";

This function below within my Excel.cs file is giving me an error of file not found:

public Excel(string path, int Sheet)
{
    //this.path = path;
    //wb = excel.Workbooks.Open(path);
    this.path = Form1.nameofexcelfile;
    wb = excel.Workbooks.Open(Form1.nameofexcelfile);
    ws = wb.Worksheets[Sheet];

}

originally, the function called the path as you see the 2 lines above commented it out. Since I want the Excel file to be found during the Form1 Textbox, how can I make this work. My error is shown below:

System.Runtime.InteropServices.COMException: 'Sorry, we couldn't find .xlsx. Is it possible it was moved, renamed or deleted?'

Error in OpenFile Function