You are quite right: math projects have a very different format than the usual science fair project. There is nothing wrong with doing a math project (unless your teacher says you can't), you just have to go about things a bit differently.
For the layout of your board, let's start with a general overview of what a science fair board usually looks like. Here is a good example:
For a math project, you might want to consider the following, modified, layout.
The "Introduction/Statement of Purpose" section could be renamed "Motivation." In this section, you would describe the mathematical problem you are trying to solve/explored and explain why it needs to be solved/explored.
The "Background/Literature Search" section should probably keep the same name. In this section, you should summarize your research and talk about what other people have done about solving/exploring the problem.
The "Hypothesis/Engineering Goal" section could be renamed simply "Objective." In this section, you should describe exactly what you expect the be able to do. For example, you have said that you are finding a formula for the Fibonacci sequence, but how do you want your formula to work? Do you want it to generate the nth term without having to generate the first n-1 terms? Or do you want it to generate a specific number of terms (like the first 300 terms of the sequence)?
The "Project Title" section is unchanged. Put your title in this section.
The "Materials, Methods, Procedures" section will also remain lasrgely unchanged. In this section (I would suggest simply calling it Methods), you should describe exactly how you went about deriving your formula.
The "Data" section should be renamed something along the lines "Proof and Examples." In this section, you should do a mathematical proof showing the validity of your formula. (Since you're dealing with a sequence, I would suggest mathematical induction as the method of proof, but this is pure personal preference.) You may also wish to show a few examples of using your formula in this section.
The "Conclusion and Discussion" section should probably be renamed "Results." In this section, you should say whether or not your objective was met (e.g. if you objective was to predict the nth term without producing all the preceding terms, were you successful?) If you achieved your objective, say so. If you did not, say so.
The "Interpretation of Data" section should probably be changed to "Implications and Applications." In this section you should discuss why anyone should care about your formula. How will it be used in real life? This should tie directly to your Motivation section.
The "Further Research" section will remain largely unchanged. In this section you will discuss what you wish to do next. (e.g. Now that you've done this project, what would you want to do if you had more time.) Do you want to improve your formula? Does your project raise any questions that need to be explored?
I hope that this helps you as you prepare your board. If you have any questions, let me know!