The entire transmission system, from amplifier output connector to the antenna should be as short as possible. Forget the attempt to match wavelength, the gain isn't enough to matter. Tune the antenna to get the best match, 1 to 1 if possible. Then use a low pass filter backed up with a tunable filter and you'll be as clean as possible. Ragged amps can create so many harmonics that a clean SWR is impossible.