Yes! I hear you! I find organizers quite horrible. I'm an 'out of sight, out of mind' person and I need things in-my-face to remember them. Also most organizers seem designed for business people juggling meetings, not a normal life.
You have two options: one, get a system and really commit to learning it. THere are lots of 'how tos' on using planners. You have to learn the new routine. The other option is to ditch the planner idea and find something that WILL work for you. I suspect that latter is the way to go, but the main thing is to learn to WRITE EVERYTHING DOWN. I mean it. DON'T TRUST YOUR MEMORY. WRITE IT!!!!
A simple alternative is a small, plain (non spiral bound - the spirals are annoying) notebook. Just write everything down.
For example: "Borrowed $20 from Jen". Cross it out when you pay. Doesn't matter where, so long as it's in there somewhere. Write your whole uni timetable in the front. Uni times don't change much, you dont' need to write them out each week.
Another suggestion: Print out your uni timetable and laminate it, or write it out on an index card (or cardboard from a cereal box) and keep it in a handy pocket. Check it often. Check it as you eat breakfast so you know what you have for the day.
Life at Uni is simple compared to life as a parent (bills, paperwork from two schools, appointments, my own classes, work functions.... yuck....) so you need to get a handle on this. I've made my life very difficult at times, by being disorganized in the way you describe. But you're not a bad person - organized people have way of making "messies" feel that way. You are a great, creative person who needs a system to help them deal with clocks and a too-full schedule.
I have a bunch of index cards cut to notebook size that I keep clipped (mini bulldog clip with fold-down handles) to the front of my notebook.
Any important stuff for the day goes on the index card. For example " -See Prof. at 3.30. Take library books back. Pick up Joe at 5." -
It's that simple, and it's there in front of you, not buried in the middle of a book somewhere. I also use them for shopping lists.
Memory and attention are influenced by our health. Consider how much sleep you are getting, exercise, and your use of alcohol, caffeine, and amount of screen/game time. At the risk of sounding like your mum...'are you taking care of yourself?'
I read a lot of Buddhist stuff, they have some very good practices about being mindful and 'present' which I find helpful. If you are distracted and mentally 'elsewhere', that isn't helpful.
Good luck!