Yes, people will still understand you if your double-R is not rolled properly (regionally, millions of natives do not really roll it), but it is important that your pronunciation of the single-R (which should *not* be rolled) and the double-R be distinct, as there are lots of minimal pairs.
Thoughtco has some good pages on the subject:
https://www.thoughtco.com/pronouncing-the-rr-3079557
https://www.thoughtco.com/how-to-pronounce-the-spanish-r-3078232
That said, the most valuable thing you could possibly do would be to master the pronunciation of the vowels. In theory, it’s the easiest thing in the world — every vowel is pronounced as in the IPA every time. English speakers have a tendency to apply crazy English pronunciation, like how the “a” is pronounced differently in every word: Hang, hand, any, wane, wan, dawn, America.