Try changing the SELECT
part of your query to be this...
select
sum(s.QuantityShipped) QuantityShipped,
s.ShortItemNo,
sum(s.ExtendedPrice) ExtendedPrice,
sum(case when aa.AccrualType=3 then a.AccrualAmount else 0 end),
sum(case when aa.AccrualType=8 then a.AccrualAmount else 0 end),
sum(case when aa.AccrualType=2 then a.AccrualAmount else 0 end)
Then remove aa.AccrualType
from the GROUP BY
.