Some/numerous cardiology fellowship programs don't even ask you to submit USMLE scores, so you definitely should not give up at this point. You could just avoid applying to programs that require the USMLE scores if yours turn out not to be so hot...I had pretty good step 1 and higher Step 2 and 3 scores, and I honestly think it only helped me minimally in the fellowship match.
You need to try and do better on Step 2, though...you don't want people to think you have a weak knowledge base. Step 2/3 test clinical diagnosis and reasoning more than Step 1, which is more basic sciency. Also, many people don't study as much for 2 and 3, so if YOU do, then I think you have a relative advantage in getting a better score (vs. Step 1, which everybody pretty much studies for).
3rd and 4th year grades and LOR's matter >> step scores in getting a good medicine residency, though with your step 1 score, you probably would have a hard time getting into the very "top" ranked IM programs. Supposing you do better on Step 2, like 220's or so, and do well in medicine clerkship and your subI, then getting into good academic programs (I'm not saying Harvard, I'm just saying solid, well known university programs) would not be that hard. Getting into a solid IM program and having some publications and getting good LORs are what will get you cards...not having high step scores, though it wouldn't hurt.