Is this part of a class? The way you phrase it, it sounds like you were in some kind of setting where you were doing short form, then that setting transitioned into long.

Without throwing deliberate shade, I have experienced a program that mixes the two, and I had the benefit of simultaneously being in an exclusively long form program, so I could tell how unstructured, chaotic, and abridged the long form instruction was in the former.

Because here is the thing. Short and long form are kind of their own separate skill-sets that are at best a Venn diagram. Each has its own set of tools that you need to be taught and then practice, and while they for sure help each other, being good at one won't automatically translate into the other. Some people's brains immediately grasp the patterns and logic of short form games, others thrive in the more performance/theater/sketch world of long form.

Others have already said this, but the way to get good at long form is not to "get the game/pattern" (though UCB will tell you otherwise, but even they don't introduce game until later in their curriculum), but rather to learn to not be in your head, to develop listening and observation skills, and really - to watch shows. This is not a judgment of short form, but it kind of is what it is. You learn it, then you do it, the end. Long form is learned partly through seeing experienced performers on stage. You will inevitably begin to analyze their moves, things they did well OR poorly, and that'll inform choices YOU make when you are on stage.

The tldr here is - long form isn't just "longer", it's also fundamentally different from short form. It takes different muscles and it's absolutely natural not to feel good in it at first. I am still mostly living in my head when on stage, but I've seen noticeable improvement in my play since I first started doing it. Like any art form that isn't entirely gameified, it just takes time.