Welcome to the forum. Please forgive the grumpy folks, but they've just heard this so many times, they think people should know better. But if you have just been exposed to the idea, and are not used to critical thinking, it does have a certain appeal. Let me guide you through where you may have been misled.

The opening premise is not really a premise, but a speculative hypothesis. To be a successful premise, it has to be based on what we actually know. We can't say "whatever" because we haven't observed "whatever," we've only observed a limited subset of "whatever". We can only speak to what we know and we are not omniscient. A properly stated argument should not inject part of its conclusion into the premise. A premise should be something that everybody knows, or that is generally accepted among experts in a specialized field.

Moreover, the expression "begins to exist" is confusing. It is not an expression you normally use, probably because neither you, nor anyone else, has seen something "begin to exist". We have observed things transformed into other things, we have seen energy interacting with matter, but we have not seen things "beginning to exist".

So let's see what a realistic starting point would be. How about this... "We have many instances of observed causation coming from natural sources having an effect on natural things. So we may reasonably say that known existing natural things can be altered from natural manipulation." This statement is based on actual observations, not our conclusion. Only it doesn't lead us to anything magical, does it? So right out of the starting gate, your argument falls flat on its face and there is no need to go further.

But just for fun, let's take it further. Why are you assuming the universe MUST have an uncaused cause? That's something to be proved, not something to be assumed. The only truthful thing you can say is that we know little about what may have brought the singularity into place. So what you have is a classic God of the Gaps argument - "There's something science doesn't know, therefore God did it." And of course, that doesn't even qualify as logic.

Thinking of uncaused causes, can you prove that your particular god did it? There may be other creator gods. Those other gods might have created your god. You see, once you allow yourself to live in the realm of imagination, Ignoring physics, anything is possible.

I wish I could stay around for any follow-up questions, but I will be away from the computer for a couple of days. I'm sure the others here can help sort things out for you.