# Should I use a correlation coefficient formula or a multiple regression formula?

I have an assignment dealing with the stock market and I'm a little lost. My instructions are to come up a method to create a score for a stock then compare the score against what the stock actually earned in 3 time periods (1 day, 3 days, and 7 days). I'm new to coefficients so I have some questions below.

Here is my data that I returned using a regular correlation coefficient formula. I swapped out the stock pct return vs market pct return and used the stock price returns for each day as the stock returns and used the score as the market return. I did this because I can create a score with information that I can get from the stock but I obviously can't get the actual return of the stock.

Score, Return, Correlation Coefficient

 26.87, 5.44, .022
21.34, 3.42, .034

1. Since I'm plugging in the data that I know and trying to get a return, does that mean I should use a predictive regression formula like a multiple regression formula?
2. Am I using them in the right place in the formula or should I swap the values around?
3. Will this matter if I swap out the values in the formula?