Coconut aldehyde mechanism
I have the impression that you a very close to find the answer yourself! 

I will not give a full answer here, but some hints.


  [...] I know I added Sulfuric acid and sodium carbonate [...]


Let's assume that you did not add them simultaneously. Then, it seems likely that sulfuric acid does the magic and sodium carbonate is added to neutralize the reaction mixture after your product has been formed.


  I am certain there is some type of internal reaction to create the five membered ring.


Good point! Let's draw the starting material and the product.

 

3-nonenoic acid is a carboxylic acid with a non-conjugated $\ce{C=C}$ double bond. With other words, there are two functional groups.

Now think in the sulfuric acid! It's a strong acid while its anion is a rather weak nucleophile.



"Coconut aldehyde" is  not an aldehyde at all, but a furanone, a five-membered lactone. Think intramolecular ester.


EDIT


Is it conceivable that the $\ce{C=C}$ double bond is protonated?
If so, what could possibly add to the resulting cation?