It's not terrible, of course, but it's not good. You won't be able to distinguish between hard and soft "r". Then, especially if your accent is non-rhotic, the sound may desappear because English "r" is less audible than Russian, isn't it? Alveolar trill is a really difficult sound. Children fight against it for a long time (I couldn't pronounce it untill I was seven years old). Soft "r" was a little bit easier to me: I started pronouncing it a year before. I managed to pronounce hard "l" only at nine. Soft "l" did noy cause any problems to me.If I can't get my tongue around it, is it a terrible thing if I'm only able to say the sound in the "English" way?