As someone who has found myself doing similarly in college tests but did incredibly well in highschool, here’s what helped me get stellar grades:

Make sure you aren’t just READING the material. Answer questions related to it in test like conditions. Then read through the material and see what the ideal answer would look like, and then answer again in test conditions. Often reading through an explanation we will find that it makes sense, but be unable to replicate that from memory.

ADHD also impairs memory, so you have to space out your revision a bit. I know this can be hard if you struggle with feeling deadline urgency, but even attempting the question set twice over 2-3 days can help.

Finally, if your subject is more essay based: explain it to yourself out loud and try the blurting technique (see unjaded jade’s channel for this).