Intervals will get you strong! Keep going at it. Ride as hard as you can, but don't hurt yourself.
And yes, the park is a great place to get a workout, much better than the streets. Before the stay at home order, you could ride the park without ever having to apply the brakes. Now it is always a lot more crowded and I find myself having to watch out. I've kind of given up on riding there, but I'll be back I'm sure. I've only been riding there my entire life and I'm 65!