* Xvimbi made his excellent post while I was typing this and I don't have time to re-do mine! Is it okay if I leave it as is? It will look like I wasn't paying attention, but I was.
I loved all the advice about walking, clapping, being steady away from the piano. I had a few other thoughts, as well.
About the trill, you can use whatever fingers allow you to be quick and graceful. At m. 15, I would do 3/1 or combine 3/2 to 3/1, and save finger 2 for the F#, but it doesn't matter what I would do-- just an example that you have options and are allowed to do what lets you be the most comfortable and musical.
About keeping tempo: you have been practicing your scales-- yea! and perhaps are comfortable doing them at very specific (fast) speeds; now, when you play this piece, no matter what tempo you establish at the beginning, those fast passages "play themselves" at the fast scale-practice tempo. Do you have the sensation that your hands are running away with themselves while you watch helplessly? If so, the first thing to do is to start practicing scales at every tempo, especially various slower speeds. The motion we make when playing something as fast as possible becomes very efficient and is not the same motion as playing the same passage slowly under control. It's often harder to play slowly once we've become fast! Yet we have to be able to do whatever's called for musically so must practice all different ways, so I think try slower scales, very even and beautiful, and really give that a chance.
Another tool is to practice ACTIVELY feeling subdivisions. In this piece, I'd start by looking at the LH in the first 10 measures. You have nice steady eighth notes at first, then suddenly longer notes and rests, no more frequent rhythms to keep everything feeling constant. Practice filling in every beat with that same rhythm: Play the LH and when you get to m. 3, start repeating the F in eighth notes (so play 6 F's) until beat 4, then play 2 eighth-notes on the F-C, and continue like that so you are "tapping" ongoing eighth notes all the way through m. 10 (m. 8 is 8 taps, the dotted quarters in m. 9 have 3 taps etc.). That is what's happening in the rhythm on a deep level, and that's what we have to feel in order to really play in time. You've probably been using a metronome to click every quarter note. I'm not much for metronomes, but if you use it to practice subdivision at first, that's probably a really good use for it. Try setting it twice as fast as usual, so it's clicking eighth notes with you, and do the LH exercise with it for a while. Slower is fine, too, you just want to practice very even eighth notes. Try adding RH to this when you're steady. After a while, you hear/feel these extra notes in your mind but don't play them.
Good luck with all that. Hope it's helpful... keep us posted!