Remember 1. Learn Hiragana, 2. Learn Hiragana? Well, now it's time for 3. Learn Katakana.
Yes, you have to learn katakana because it's used everywhere. Why is there a katakana syllabary? Why can't we just use hiragana for everything?! Because katakana is used to spell loan words, i.e., words which are borrowed from languages outside of the native Japanese language. It's not that bad since we already know what the sounds of each of the katakana are because they're the same as those for the hiragana.
So, if you've memorized all the sounds for each of the hiragana — and I know you have — , you're all set for katakana. Sort of. The sounds are the easy part. I find the shape recognition a little harder.
You see, katakana is more, shall we say, minimalist in design than hiragana. With all the loopy thingies in hiragana, it's easy to tell one hiragana from another. With katakana, the minimalism can make some of the kana look the same. Even now I confuse ワ with ウ and others which have a similar shape. I know I shouldn't but I do. I usually figure out which one it's supposed to be by the other katakana used in the word. When I mentioned this "technique" to my son who's been studying Japanese for awhile, he replied, "Yeah, so do I."
Over a year ago, I had complained loudly to a group, "I have such a hard time with katakana!" A Japanese native shot back, "So do Japanese!"
Now these stories aren't meant to be free license to ignore katakana. Even if we who have studied katakana have trouble reading them, we still know them a lot better than most people so please try to learn them as solidly as you can. If it's not perfect, it's okay. We'll all get there one day. Even writing that I mix up ワ with ウ has made me realize that, oh, of course that's ウ and not ワ. I got this.
My favorite way to learn katakana is by following the instructions in Tofugu's Learn Katakana: The Ultimate Guide. It's just as methodical and fun as their Ultimate Guide to learning hiragana. Play the free games they list there. Play them again even after you've conquered 〜て form ...
At the very least, learn how to write your name in katakana (if your name isn't Japanese). My name is so long that I automatically know how to write 7 out of the 46 katakana ( ~15%). When I was in Japan staying in hostels, I practiced writing my name in katakana whenever I labeled my groceries. In Kanazawa, a group of us were introducing ourselves at the kitchen table. When I started to air spell my name in katakana, a Japanese native said, "Oh, yeah, I already know. I saw your name in the refrigerator."
At the very least, learn how to write your name in katakana (if your name isn't Japanese).
oh, and fun fact, if you know English and can read katakana, then you'll automatically know or can figure out about 25,000 English loan words in the Japanese language. That's incentive. :)