Anki is not a basic flashcard app, but a spaced repetition app. Thus it is a design choice to actively discourage users from cramming. It is, however, no problem to set up cramming with a filtered deck. Create a new filtered deck, enter the search string “deck:DECKNAME” (or “deck:current”), select 9999 cards (to filter out all the cards), enable random selection, deselect “Reschedule cards” and build the deck. Rinse and repeat.
https://faqs.ankiweb.net/anki-is-not-showing-me-all-my-cards.html
If you have a test due in a few days, it’s probably not the best time to be starting with Anki. While Anki does have tools to bypass the regular scheduling for things like upcoming tests, they take some time to learn how to use, and they are awkward to use on a daily basis. If you have an imminent test, you may want to consider studying as you have done previously, and then picking Anki back up when you’re not under as much pressure.