Help! I sliced my flank steak along the grain, is there a way to still have tender meat? I don't know how to cook beef, I'm really not a meat eater; however, I prepared a recipe from memory and I was in a rush and I thought I remembered reading to slice the meat along the grain...I was wrong. I see articles all over the internet about how to slice it correctly, but I don't see any articles about what to do to salvage your meat when its sliced incorrectly. 

Right now my meat has been marinating for about 16 hours and I have 8 more hours to go. Is there anything I can do to this meat to guarantee that it'll still be tender, even though I sliced it wrong? I am making Hunan beef by the way. Thank you in advance for your responses.
I will shamelessly steal @Jolenealaska's thunder and recommend velveting your meat as a means to protect against overcooking.  This is a great method to bring meats just up to temperature, and is a very traditional preparation for stir-frys.  Should work nicely with your Hunan Beef.