Querying DynamoDB - results in the wrong order

I have a table where the primary index is keyed on attributes called "PK" and "SK". Currently, there are three items in the table

When I run a query on the table, using the following C# code (where searchTS = "DASH-20221209-23:32:11") I would expect to get the 3rd item in the table (as that is the one with the value of SK <= the searchTS value). I actually end up with the 2nd item.

            DynamoDBContext context = new DynamoDBContext(_client);

            var searchTS = $"DASH-" + DateTime.Now.ToString("yyyyMMdd-HH:mm:ss");

            QueryFilter qf = new QueryFilter();
            qf.AddCondition("PK", ScanOperator.Equal, "STAT");
            qf.AddCondition("SK", ScanOperator.LessThanOrEqual, searchTS);

            var opConfig = new DynamoDBOperationConfig()
            {
                OverrideTableName = "ClinMod-Analytics",
                BackwardQuery= true
                
            };

            var queryConfig = new QueryOperationConfig()
            {
                Filter = qf,
                Select = SelectValues.AllAttributes,
                Limit= 1,
            };

            var docs = await context.FromQueryAsync<Analytics>(queryConfig, opConfig).GetNextSetAsync();

            return docs[0];

I have tried flipping the value of BackwardQuery but that does not appear to change anything.

What am I doing wrong?