I have a 20 gallon tank and the heat side doesn’t ever get any higher that 95 degrees. I know it’s best for it to be 100-105. At the moment it’s a 75 watt zoomed basking lamp. I was wondering is a 100 watt would be too much?
You might be OK with a 100w. You could hang it from an adjustable lamp stand and just set it a bit higher up which will adjust the temps across the tank. Are you measuring the surface temp on the basking area or are you using a thermometer reading air temp? Those can be quite different and surface temps should be used for adjusting lighting.
Try leaving the probe directly on the basking spot for 30-45 min or so and check the temp and see what you get. The surface temps might be good enough as-is.
That's still a bit low. I'd try a higher wattage and maybe raise it up a bit or go to a halogen and use a lamp dimmer to fine tune the output a bit and try for 100-105.