You meant your weight is 120 pounds, right. If yes, I feel you are absolutely fine. 120/80mmHg is the average reading in a normal adult. It varies daily by a few mmHg here and there. Your Blood pressure reading is absolutely normal. Continue with the healthy food and exercise.
It is always best to have a complete general check up as a routine maybe once in a year or so. The tests should include Complete blood picture, Renal function test, Liver
function test, Fasting lipid profile
, Fasting and post prandial blood sugar levels, Baseline ECG.
Don't worry about your BP reading, it falls within the normal range.
Have a nice day :)