not sure what my best interests are.

The city is most likely not liable to you: for them to be liable, you would have to show three things--that they were unreasonably careless in where they left the gravel (which may be difficult--it's reasonable for some loose gravel to be left behind during/after repairs); that the gravel caused your fall; and that you were not yourself careless in standing on the curb, on loose gravel, while turning on your mower (since if an injured person is careless, too, his or her own carelessness can reduce or even elminate what he or she could recover). You need the city to be careless, the gravel to have caused the fall, and you to not be careless to potentailly recover.
Even if the city is liable, it's not clear that a lawsuit is economically worthwhile. You can only recover in a lawsuit the sum of: 1) your out-of-pocket medical costs (costs not paid by insurance); 2) lost wages (if any) due to the injury; 3) for *long-lasting* injuries which cause *significant* disability or life impairment, some amount for "pain and suffering"; and possibly any property (e.g. shirt) damage. But to recover for pain and suffering, you'd need to hire a medical expert (e.g. doctor) to examine you, write a report, and testify, if necessary, at trial, which can run hundreds into the low thousands of dollars, and you can't get that cost  back from the other side; therefore, even if they were liable and you sued and won, if you don't have a major, long-lasting injury or large, out-of-pocket medical costs, you could spend more on the lawsuit than you get back.