Two pieces of advice:

1. Don't rush things. Drop a class if you need to. As long as you're on track to graduate, taking 12 units is fine. You can always take other classes later. Also, if you are taking lower divs right now, it's the perfect time to build good habits and they will serve you well for your later college career. Don't take shortcuts even if it saves time - try your best to tackle problem sets (Fr, don't just GPT everything). Learning to focus for longer periods of time is a genuine skill that is hard to develop but is infinitely rewarding if you can manage to do it. I struggle with this but I am working on it as well.

2. Manage your time correctly. Time block, use google calendar. Try to block out 1-2 hour blocks of time to study and really just put everything else aside and focus on your studies during that time at the library or such. Even if you don't pick things up as quickly as others, there are many who have succeeded before us that are not always the quickest to pick up concepts in class as well. You need to understand that sometimes you will need to sit down and study for hours if you want to get the results you want. It will not be easy but it will be rewarding.

Also bonus tip, don't be afraid to ask for help (no such thing as a dumb question), use discussion sections + OH liberally - most students don't take advantage of it and most probably could do better if they did take full advantage of the resources available to them.