@SeasonsGreeeeetings -
Speaking as an only, who had a small family, and no cousin until I was 16 (whose parents then, within the year, distanced/estranged themselves from us for reasons unknown - they also don't contact any other relatives anymore)...
I used to have a lovely day. I never felt I was missing out - I knew no different. I loved spending time with my close family (there were 4 of us for the main day, an extra 2 for Boxing day until my cousin was born), and that was just...how it was.
I have wonderful memories of growing up and Christmas holidays, the Monopoly wars we had, the enjoyment and inclusion and just... yeah.
I mean this in the nicest and most inoffensive way - this stress and worry is a you problem. And it is entirely natural as a mum and parent to worry and compare to your own experiences... but from me and mine - there's nothing to worry and stress about.
And I know, from speaking to my mum now I'm (apparently) an adult, that she had/has worries similar and that things weren't enough. But they were :)
So have a sit down, a cuppa, and give yourself a smile and pat on the back. The mere fact you're worrying shows how much you care, and gives me a strong feeling of how much love and care your Only has had today (and every other day as well!)