Indicate that you want to cooperate – fully. But ask for time to calm down and to call your attorney. You'll need to lose the adrenaline and process a life or death event. Most people involved in shootings can't recall seemingly simple facts like the number of shots they fired. Trying to be helpful before your brain has processed what just happened may end up getting you in trouble even if you did nothing wrong. If you say you fired twice but forensics later shows that you fired six times in the heat of the moment, it might not look good for your case. It's more important to relay the facts accurately than immediately.
Be clear that you were attacked. Many trainers recommend saying that you're willing to sign a complaint. That shows that you are the victim, not the aggressor. Of course, it will all have to be proven later.
Consider identifying and getting on retainer with a local attorney experienced in self-defense law – now. You won't want to be looking for professional assistance at 2:30 a.m. on a Tuesday morning while you're on your way to jail.
Better yet, join a self-defense protection network. As an example, the USCCA offers membership plans that provide immediate 24x7 legal assistance, bail funding, legal funding, and much, much more. There are several similar plans on the market, so do your homework on the best fit for your needs.