I would love to be able to say "yes, you would be sure"
But that's just not true. Some people have very small "silent heart attacks". The key thing fhestia mentioned is recognizing "textbook symptoms"". Well, those textbook cases are not all that you see in the real world. I won't go into detail to give you more to worry about but there are multiple potential presentations of heart attack. Generally females, elderly, chronically ill, various races, may respond with different than textbook symptoms.
The good news? You are 18. You are athletic. It would be VERY rare for you to have a heart attack. Especially if you are not diabetic, and don't have a family history of heart disease at a very young age. If you don't smoke or use cocaine, great. If you do....stop.
What you describe is likely inflammation of some of the cartilage on your chest wall or a muscle strain. The fact that it's tender to touch suggests musculoskeletal cause. However, "persistent" is always something you want to get checked in on, in particular if you're having pain with breathing or the pain gets worst when you lay down. I'd recommend getting checked out by your doctor tomorrow morning if you're not feeling better, or go to the ER
IF the pain becomes more intense tonight.