Advice on choosing offers. "Staying in the system"

For my UCAS application, I have been accepted by a few universities but it turned out that what my college referred to as A Level maths was Core Maths (math at A Level standard, but not constituting a Maths A Level) meaning that I had to send out emails to universities telling them of this error. Only one university told me that they would still accept me after this.

Then I realised that I could use Distance Learning & Fast Track to earn a maths A Level during a gap year I was and still am going to take, and I have decided to do that so I can be admitted into a better Computer Science university. However, my offers still remain and I'm not sure what to do.

Then my parents come in. My parents have been very vocal about how I should accept the non-A Level university and defer: to condense a lot of annoying rhetoric and vehemence, they say that if I accept the offer and defer it will "keep me in the system" and I don't have to go and can approach a more prestigious university later. However, I have read on UCAS's own website that if I am secured a place at that university I will be COMMITTED to it unless otherwise negotiated (if it is even possible to do so) []https://www.ucas.com/undergraduate/applying-university/when-apply/deferred-entry].

I don't know what to do. I desperately want to go to a decent university and am willing to put the effort in, but I'm in constant fear that a misstep will force me into the wrong direction with no way to return: I want to put the effort in that I know I can do and have been doing intermittently, but I don't want to feel like my life is crashing down on me. I just want to ask for advice on what to do.

The issue with this plan is that whilst holding a deferred place, you cannot reapply to UCAS in that cycle. The deferred entry system exists to offer people flexibility to take a gap year, not to secure a back-up for the next cycle.

I have been thinking if I should simply reapply to UCAS next year with my expected A-Level maths grade, but I'm not sure if I'd be able to convince my parents (especially this close to the deadline). I have contacts (and now that I think about it, will likely have more with the A Level) that will be able to give me a reference if I need to submit again.

Even if my A levels go poorly I could apply to the university that doesn't ask for A Level maths again. Except it would be even easier with a gap year's experience of having a part time job and independent study (that I hope my parents will follow through with).