The combination of cornstarch and strawberry gelatin combine to create a thick glaze for the strawberries. It may be a little runny, but should not be overly runny. If your completed pie is very runny, here are a two reasons why: 1) it did not chill for a full 6 hours OR 2) the cornstarch mixture didn't come to a full boil. If it's the former, let the pie continue chilling until set.