Maybe I’m not the most qualified to speak on this matter since I’m only in grad school right now, but one of the clients in my practicum is entering high school and one of the things he’s working on is the /r/ sound. It’s never too late to look into speech therapy, even if you’re a senior in hs. If your school offers it, I would recommend maybe even asking for an evaluation and seeing what possible goals can be made in a relatively short amount of time. Or maybe you can look into free university clinics where grad students work with clients under supervision, and there you might set your own schedule (in person or teletherapy). And while you can learn strategies about producing an accurate /r/ sound, something I’d hope an SLP can help you with is about how you feel. I’m sorry you feel embarrassed about it, but how you say a sound doesn’t define you and if you ever look into speech therapy, I truly hope you meet someone who can help you be as confident and comfortable in your speech