Get there like an hour early. Anymore is just overkill. (unless its peak travel season or international - which its not). You dont have to check in any of your bags (both carryon). As someone said, you will put the gym bag up top and you can keep your backpack in front of you. Aisle isnt that bad bc you can stretch out more, though Im sure you would appreciate the view. If you wanted though, once you have boarded the plane, you can offer to switch seats with someone. Im sure there are people that would rather sit aisle than window, and there are no rules against swapping. Oh also, you can talk to the agent at the desk and ask to change seats too.
Remember, flying is safer than driving! If you encounter any turbulence dont be scared. Up in the air, the littlest bounce will feel like a lot. But just think of being in a car, if you hit a bump or pothole you get pushed all around too, but you arent worried about crashing! Its the same with flying, just the feeling is foreign.