Few tips.

On rollers with no resistance (which I think is best for me), use the biggest gear possible. Since resistance is pretty low overall you should be able to go 30 mph without problems. The faster you go and the lower the rpms the more stable you'll feel. Doing a 53x11 at 80 or 90 rpm is pretty mellow. Doing a 39x23 at 120 rpm is really nervous.

If you are nervous on rollers, try doing a hallway instead of doorway. Put the rollers near one side, maybe 6" away? Close enough that you start brushing the wall if you get too close to that side. Use a chair or something on the "open" side. Keep bumping the wall with your elbow/shoulder/hips. You can even lean on the wall.

Don't have any glass things nearby. Glass (for water), glass table, screens, etc. It's amazing how much force you put down when you are reaching to grab something as you topple. You can easily crush a glass in your hand.

Low tire pressure can build up heat in tires. An old trick is to put an old towel under one of the rollers.

If you have a Schwinn dealer near you, you can get AirDyne fans. They mount to a spoked wheel and create significant resistance. As a bonus they cool you down. You might find an old AirDyne for cheap/free and strip the resistance blades off.

If you are nervous but okay pedaling, do some high rpm accelerations, then coast. Try not to bounce. Doing higher than normal rpms will make slightly higher than normal rpms seem smooth. When I need to work on my pedal stroke I get on the rollers, try to do 120 rpm for an hour. I can't now but used to do it with shorter cranks (I can do 105 rpm for an hour). 120 rpm is a bit high for efficiency, but it makes the optimal cadence (anywhere from 95 to about 110-112 rpm) much easier.

When you get better at rollers, do the spin up but don't coast, follow the pedals as the wheels slow down.