I'll let you into a secret. I hate katakana.
Students of Japanese tend to start with its two phonetic alphabets. We start with hiragana, the loopy, flowing letters that make up all the sounds of Japanese.
Then we move on to katakana - all the same sounds, but in angular blocky font.
Hiragana seems fairly easy, I think. And when you start learning Japanese everything you read is written in hiragana, so by reading you constantly reinforce and remember.
Katakana? Not so much.
The katakana "alphabet" is used extensively on signs in Japan - if you're searching for カラオケ (karaoke) or ラーメン (ramen noodles) you'll need katakana.
But if you're outside Japan, then beyond the letters in foreign names, you don't get a lot of exposure to katakana.
I think that's why a lot of beginning students really struggle to remember katakana.
Here are a couple of suggestions:
1) Use mnemonics
Personally I still can't remember some of those sticky similar katakana without goofy mnemonics
For example, I still think katakana ウ (u) and ワ (wa) look super similar - I remember that ウ has a dash on the top, just like hiragana う (u) .
2) Practice, practice, practice
I'm not a huge fan of having you copy letters over and over again, but there is something to be said for "writing things out".
By writing letters down, you activate muscle memory, which helps you remember. So get writing katakana!
3) Start learning kanji
It might feel like running before you can walk, but starting to read and write kanji (Chinese characters) before your katakana is completely perfect can be a good option.
Kanji textbooks have the Chinese readings of the characters in katakana, so learning kanji is also really good katakana practice.
And maybe, you'll turn into a katakana lover, not a hater.