AK, you didn't mention what engine/prop combination you are using. This airplane set up per the plans should slow down very nicely. If you've changed anything from the plans the above ideas are good things for you to check.

But most of the time when people can't slow a plane down the problem is technique. What is your flying history? As Steve asked, is this a move up to a more advanced airplane? You have to remember, your Katana isn't going to be as draggy as a trainer or a stick so it's not going to slow down as quickly. And flaperons definitely isn't the answer. We've all played with them at one time or another and most all abandon them as not a good thing. As you have discovered they make the plane non-responsive right when you need the response the most. And if you do use them, 25 degrees is way too much.

The usual answer to this problem is to slow down your plane sooner and start your descent sooner. A light, slick airframe has a much shallower approach angle than a draggy airplane. If you try to come in too high, when you force it in you will gain airspeed that you can't bleed off until you're past the runway.

When I prepare to land I chop my throttle back to just about 3 clicks above idle on the downwind leg about directly in front of me. That's right, still have half a circuit to fly and I'm almost at an idle. Let the plane descend during the downwind leg. Do be careful of your turns as you're flying slower now make gentle turns and watch for stalls. Keep the nose down in the turns and you'll be bleeding off altitude. When you come out of your final turn you should be much lower than the approach you make with a stick or a trainer. If you're too low, add a little throttle to stretch the approach. As you approach the runway continue descending and cut throttle even more. That plane should be able to slow very nicely but it will require throttle and altitude management.

The last thing is to practice. Get out to the field when it's not crowded and practice touch and goes. One after another. Entire flights of touch and goes. Don't be afraid to put the power back on and go around if you're coming in hot. If you do enough touch and goes you'll find the technique that works for you and your plane.

Dave