Who are the experts? They're the people more senior, more experienced and more informed than you.
Don't fear them. Use them, with appreciation and pleasure.
Adopting the right attitude can make all the difference
It is that simple, but it won't be easy until you adopt the right attitude. Most beginners think being caught not knowing something is a credibility disaster, but that's almost never true. What matters more is your reaction to not knowing. Even the most technical audience is impressed when you're confident and poised in the face of a setback or challenge - that response outweighs your junior status, inexperience and lack of knowledge.
Here's how to get that confidence and poise.
From the beginning of your presentation
Adopt this attitude:
When the expert begins to speak
Choose this thought pattern: Ah, how can I make use of this for everyone?
So, right away, what does the audience see in your expression? Appreciation and pleasure. The expert is about to add a perspective you may not already have.
When the expert disagrees with you and you still believe you're right
Say "Thank you," and mean it. And you might add, "Would you like to expand on that?" (Glance around as you say this, making it clear that your motive is to look after the audience.)
When she has finished, thank her again, then continue with your argument. Valuing an expert's input is important, but it does not mean that you have to change your mind.
When the expert disagrees with you and you realise that he's right and you're wrong
And here's the one most junior staff dread. The expert disagrees with you and you realise that she's right and you're wrong - and that it's something you really should have known. The answer is surprisingly simple.
Say, with a nod of genuine gratitude, "Thank you, I didn't know that, and I should have." Then continue, changing direction appropriately. Your audience knows instantly if you try to dodge or disguise lack of knowledge.
Do you see the implications? It's not just about being honest and open. You must choose to be relaxed about your own lack of knowledge or experience, treating it as just another part of your development. Choose to say to yourself, They can see through me and that's okay. Choose to have the courage to be imperfect.
To be relaxed about your weakness is a strength. Your audience will be very impressed.