Every day, you do a hundred or a thousand jobs, some of which are occasionally handled by specialists. You make a sales call or give a presentation or answer the phone... you design a slide or create a simple spreadsheet. You get the idea.
When you are busy being a jack of all trades, you're competing against professionals. The recipient of your work doesn't care that you are also capable of doing other things. All she wants is the best she can get.
I'll define a professional as a specialist who does industry standard work for hire. A professional presenter, for example, could give a presentation on anything, not just the topic on which you're passionate about.
When you compete with professionals, you have a problem, because generally speaking, they're better at what they do than you are.
I think there are four valid ways the think your way out of this situation:
Hire a professional.
Be as good as a professional.
Realize that professional-quality work is not required or available and merely come close.
Do work that a professional wouldn't dare do, and use this as an advantage.
The first option requires time and money you might not have, and I'm presuming that's why you didn't do it in the first place.
The second is a smart option, particularly if you do the work often and the quality matters. Slide design and selling are two examples that come to mind here. The first step to getting good is admitting that you aren't (yet.) Invest the time and become a pro if it's important.
The third option is worth investigation, but it's what you've probably already decided without putting words to it. Is the assumption really true? Does your customer/client/employee actually believe that they haven't been shortchanged by your amateur performance? It is costing you in ways you're not measuring because you're willfully ignoring the consequences? Think of all the sub-pro experiences you've had as a customer, instances where someone was pretending to be a chef or a bartender or a computer jock but just came up short... Were you delighted?
The fourth option is really exciting. From personalYouTube videos to particularly poignant and honest presentations or direct and true salespitches, the humility, freshness and transparency that comes with an honest performance might actually be better than what a professional could do. Harvey Milk was an amateur politician, not a pro. If you're the only person on earth who could have done what you just did, then you're a proud amateur.
You can't skate by when you refuse to mimic a professional. You must connect in a personal, lasting way that matters. That's difficult, but the professionals have no chance to compete with you.
Be an amateur on purpose, not because you have to.