How to handle an SQL DB Bit value

I have a table that has a column (IsParticipant) that is set as a BIT type that can be NULL, 1 or 0.  The intent is to use the NULL to determine if the customer has made a selection, i.e. Yes or No (Radio Buttons on web page).

I have a stored procedure that is used to get the field IsParticipant. 
ALTER PROCEDURE [dbo].[X_GetParticipantForXAndY]
    @xID uniqueidentifier,
    @yID uniqueidentifier,
     @IsParticipant bit output
   
AS
BEGIN
    If @xID is null
    BEGIN
        RaisError('xID must be provided.', 16, 1);
        Return 1;
    END

    If @yID is null
    BEGIN
        RaisError('yID must be provided.', 16, 1);
        Return 1;
    END

  
    SET NOCOUNT ON;

    SELECT @IsParticipant = DS.IsParticipant

    FROM DShows DS

    WHERE DS.xID = @xID and DS.yID = @yID;

END


I then have a class method that calls the stored procedure and then I want to use that NULL, 1 or 0 to set the True or False settings for the Yes and No Radio Buttons.  If the value is null I want both radio buttons set to false.


sqlParameter = sqlCommand.Parameters.Add(new SqlParameter("@IsParticipant", SqlDbType.Bit));

sqlParameter.Direction = ParameterDirection.Output;

SqlHelper.ExecuteNonQuery("X_GetParticipantForXAndY", sqlCommand);

My initial thought was to have the method be set to return a Boolean.

My issue is, I am having problems returning the null, 1 or 0 back to the web page class -
Boolean isParticipant =  Webpg.GetParticipant(xID, yID)

Based on how I setup the return statement, I can either get the null passed or the 1 & 0 but not the three values.  What am I doing wrong?  I am new this type of environment and it has been years since I have programmed with other OO Language.

I have tried these three return statements:
return Convert.ToBoolean(sqlCommand.Parameters["@IsSHSLogParticipant"].Value.Equals(sqlCommand.Parameters["@IsSHSLogParticipant"].IsNullable));

return Convert.ToBoolean(sqlCommand.Parameters["@IsSHSLogParticipant"].Value);

return Convert.ToBoolean(sqlCommand.Parameters["@IsSHSLogParticipant"]);