This new 1-match placement is crap. Even more than before. I placed into Platinum Rank 24 after one match against some horrible protoss after I hadn't 1v1'd for like 2.5 months. I placed into Platinum in 3v3 after losing my placement game to triple diamonds. Maybe when the ranking system makes more sense and I can get a grasp on how good and/or bad I actually am I could consider such a service.
Season 3?
How many games have you played? If you haven't played enough games, your league might be off and won't be adjusted until your predicted win rate matches your actual win rate to within a certain margin. After that, you'll be amazed to find that the matchmaking system is exceptionally good at matching people around your skill level, and your league will eventually reflect what that actually is.