May I suggest that your anxiety is the problem, not the mortgage, if this is making you unwell. You are setting yourself an impossible goal its seems, and then getting in a state about not being able to achieve it. This is not a rational thing to do.
Lots of single parents have mortgages and unreliable incomes, and still have happy lives. And while this kind of debt feels huge it is spread over a long time for this reason. As long as you pay regularly when you can, the bank will be reasonable if you get into difficulties - they don't want to manage repossessions, they want you to stay there and continue to pay when you can. Most people don't pay off their mortgage until later in life middle age or near retirement, and as house prices increase, mortgage periods are getting longer and longer.
You need to take a deep breath and think about this in a more constructive way. You are in many ways very lucky. You are not renting and having to deal with being given huge rent increases or being evicted every 6 months. You have a stable home, and a way of paying for it right now. You have a debt that lots of people manage on their own - single people, single parents, widows and widowers. Banks are in many ways more accommodating of difficulties than landlords. You have your lovely daughter.
Your daughter would much rather have a happy mum-please don't teach her that she is the cause for anxiety and financial worries. Kids pick all this up even if you try to hide it.
There will always be people better off than you. Please don't compare yourself to other people, comparison is called 'the thief of joy' for a good reason.
Please don't worry about a future that you can't predict and can't change. That will only make you both unhappy.
And if you can't let some of this anxiety go then you maybe need to recognise that this might be a symptom, not a rational worry, and see a doctor or a therapist.
I hope you feel better about this soon.