Dapper/SQL Server - get output from Stored Procedure containing Insert and Select statements

I just started learning Dapper in C# but I am having difficulty in executing stored procedures with two or more SQL Statements in one transaction.

How do you get the output parameter of a Stored Procedure that contains both Insert and Select statements in C# using Dapper?

Here is my stored procedure:

ALTER PROCEDURE [dbo].[AddToFileDetailsAndGetPrimaryKey] 

-- 1. declare input variables
@file_name NVARCHAR(100) = NULL,

-- 2. declare output variable
@file_details_pk UNIQUEIDENTIFIER OUTPUT

AS

-- 3. instantiate holder table
DECLARE @pk_holder TABLE
(
    retrieved_pk UNIQUEIDENTIFIER
)

-- 4. insert into FileDetails
INSERT INTO dbo.FileDetails
(
    file_name
)
OUTPUT INSERTED.file_details_pk INTO @pk_holder
VALUES
(
    @file_name
);

-- 5. set FileDetails primary key to OUTPUT variable
SELECT @file_details_pk = retrieved_pk 
FROM @pk_holder

Here is the code I'm using to execute the stored procedure:

using (IDbConnection connection = new System.Data.SqlClient.SqlConnection(Configuration.GetConnectionString("TESTDB")))
{
    List<FileDetails> fileList = new List<FileDetails>();
    fileList.Add(new FileDetails { file_name = fileName});

    Guid outputPrimaryKey;                    

    connection.Execute("dbo.AddToFileDetailsAndGetPrimaryKey @file_name, @file_details_pk", fileList, outputPrimaryKey);
}

Is this the correct way to do it? Should I use connection.Execute or connection.Query? I am also getting an error of "cannot convert from System.Guid to System.Data.IDbTransaction in my outputPrimaryKey"