You are going to have a real problem because ASTROLOGY IS NOT A SCIENCE. It is a fortune telling system based on myth and superstition. Not testable evidence.
Your science teacher must have explained the scientific method to you.
The scientific method is the best way yet discovered for winnowing the truth from lies and delusion. The simple version looks something like this:
* 1. Observe some aspect of the universe.
* 2. Invent a tentative description, called a hypothesis, that is consistent with what you have observed.
* 3. Use the hypothesis to make predictions.
* 4. Test those predictions by experiments or further observations and modify the hypothesis in the light of your results.
* 5. Repeat steps 3 and 4 until there are no discrepancies between theory and experiment and/or observation.
When consistency is obtained the hypothesis becomes a theory and provides a coherent set of propositions which explain a class of phenomena. A theory is then a framework within which observations are explained and predictions are made.
A theory is accepted not based on the prestige or convincing powers of the proponent, but on the results obtained through observations and/or experiments which anyone can reproduce: the results obtained using the scientific method are REPEATABLE. In fact, most experiments and observations are repeated many times (certain experiments are not repeated independently but are repeated as parts of other experiments). If the original claims are not verified the origin of such discrepancies is hunted down and exhaustively studied.
Because astrology is a belief oriented, it can not use the method. However, it's claims are fully testable and all testing has shown that it fails to do better than chance.
The sign change is nothing to worry about. You choice of subject was wrong from the start for a science fair. You want real science? The second link shows why astrology can't work.
Edit: Which astrology is the real one? How is this known? There are many types and each one contradicts the other. Science is neutral method that uses evidence and not belief. If you don't believe in gravity, does it cease to have an effect?