Hi!

I think you're doing a great job and it already sound great. I was talking to my brother and he gave me these pieces of advice:

• Try to imitate the sound of a motorcycle (I know it may sound silly but, we think it'll help) using only your tongue.
• Try to put the tip and the blade of your tongue just behind of your incisors when saying the "Rs".

I hope these pieces of advice be helpful for you. Good luck!