First of all, congratulations that you did it, that was a big step !
I had similar issues a few years back, shaking hands, heart racing, etc. but was able to improve that quite a bit. For example, two weeks ago, at a horse riding event in South Dakota, I got my keyboard out and played for about 10 people for about 30 minutes. I was a little nervous at first, but it was still o.k.
The tricks that I use are the following:
a) I often play when I know how many folks will be around. If there are just a couple of folks, then I am mostly good. I also know beforehand whether people are intently listening or whether they are busy with something else. So, to lower my fear threshold, I seek out situations where my playing is not the only event. Ride camp is perfect for that <-: This slow exposure to an audience helped me a lot.
b) I generally start out with warm-up exercises. These are sequences that I use also to warm-up at home, I know these by heart and don't need any sheet music for them. These are, for example, chord sequences I-Vi-V-I, hands crossing over in several octaves, also variations of chord sequences, etc. This takes about 5 minutes. Sometimes I change these up or modify them on the fly. Sometime I just change the rhythm of the same sequence or add walking bass steps. You and I may know that this is not a real song but instead only an exercise, but the audience may not know that.
c) I have about 300 songs in my repertoire. It is a mix between piano solos, lead sheets, and chord sheets, they all serve different purposes. The main thing is that when I feel during the warm-up that I am nervous, I will drop my playing level several steps lower. That means I won't play any piano solos. Instead I play from lead sheets ... simple melody in the right hand, chords in the left hand. If that is not low enough, then I play only the songs that I got in C major or any other key signature that I can easily play. In other words, I can drop the difficulty of what I play "on the fly" and thereby I regain confidence, and after awhile I can consider increasing the level of difficulty again.
d) In an informal setting, there is no obligation to play a song to the very end, or every part of it, if that gives you trouble. You can gracefully terminate a song within a couple of notes if the actual ending gives you trouble.
e) Improvisation: Making this part of your daily routine helps you to "make up" sequences, tone combinations on-the-fly and helps when you forget where you were in the sheet music, just adapt a little, gracefully terminate and then go to the next song. When improvising in your daily routine, turn on your favorite drum loop and just start playing something within the chosen key.
f) Observe your audience: if your audience are passersby and it is not the same folks, you can repeat songs, particularly the ones that you know you can play well.
g) Another trick on a digital keyboard/synth is to layer sounds, e.g., strings, etc. and add a little sustain. If you then play the melody only with your right hand, that could tide you over until you feel more confident. There are also automatic arpeggiators on some digital keyboards that you can experiment with. Those can add sound while really pressing just a simple block chord with your left hand.
Keep us updated and wish you all the best.