Ideas:
1. Ask your uncle privately to not try to ruin your performances. Explain to him that it isn't a game where he is supposed to try to figure things out. Explain that by doing what he is doing, it makes you not want to perform.
2. If that doesn't work, don't perform for your uncle or if he is around. If anyone asks, just explain that it isn't fun for you to perform when your uncle tries to ruin it for everyone.
3. Change your performing style. Most of these problems result from performing "tricks" with nothing more than a presentation that narrates what you are doing with the props. If you are only talking about what you are doing, the audience is going to focus on how you are doing it. Also, evaluate your style to see if you are inadvertently presenting magic as a contest where you try to fool the audience (i.e. make a fool out of them) and they react by trying to "catch" you.
4. Develop audience management skills. As a magician, you are responsible for having total control over your environment.
~If a spectator asks to handle the cards, the answer is no. The the spectator asks to shuffle, the answer is no. If the answer is to see the card that is inserted, the top card, the bottom card, the card on the table, the card in your pocket, etc. the answer is no. EVEN IF THERE IS NOTHING TO SEE!!! If you let them control your performance when it doesn't matter, you lose control when it does matter.
~If you give the spectator an instruction, tell them what to do by saying "when I tell you to, I want you to help my by [insert instruction]." Then ask them "do you understand what you are going to do?" or "will you do that?" Then say, "OK, I want you to [insert instruction] now." They hear the instruction, consent to it, and then hear it repeated.
~Control where you put props. They should be within your sphere of control, so that you can grab them before the spectator can get to them.
~Don't pick people who look like they may be trouble to help you. Pick someone else. If the potential troublemaker tries to interfere, just say, "I'm doing this with [insert name of other person], I'll do one with you later." You decide when later is (next effect, next day, next month, next year, etc.).
5. Perform effects where the spectator is the hero. If they think you are going to make them look good, they won't screw it up. Remember, their goal is to be the center of attention. Now, this needs to be done after #1 through #4, especially #4. It won't work if you are not in control of your environment.
6. Focus on openness, design and presentation. By openness, I mean the motions you make with your hands need to be relaxed and have an open feel to them (one of the ideas of the Madrid School that you will find in Giobbi's Card College). Also, make sure your attention is not on your hands. Many people who have learned from YouTube learn slights that have a closed feel to them (quick motions, smaller motions, lots of tension, etc.) and focus on their hands (because every YouTube video focuses on the hands, it is only natural to look at your hands because that is how you learned it). Also, get over magician's guilt. Many "intermediate" magicians get stressed when they are "dirty" and it draws attention to that moment. Enjoy being "dirty" and make sure you don't act differently if you are pushing their card or a card you swapped out into the deck. By design, make sure the design is fair. Build in opportunities for the spectators to observe the fairness (e.g. showing the deck as shuffled, letting them shuffle before the effect if it doesn't matter, having them push the card into the deck if it doesn't matter, etc.). You are showing them fairness on your terms so they don't demand to be shown the fairness on their terms. For presentation, make it more that say-do-see patter. If you engage their brain with the presentation, they will focus less on the how.
7. There is a reason this one is last, because it just escalates the issue by trying to come up with things that your uncle can't figure out so that you win (i.e. he is the fool because he can't figure it out) unless you do #1 through #4, especially #4. Get Scarne on Card Tricks. It is all self-working and they are great effects.