The problem is not with the size /wattage/BTU of the heaters. Two thermostats are involved. One is the wall thermostat. It may be inaccurate. What is the highest available setting on it? Have you tried that setting?
The second control is a self-resetting high limit "thermostat" built into the heater. It limits the temperature within the heater to 156 deg F. to limit injury to those who might place fingers into the heater and to lessen the chance of combustion of accumulated lint, rugs or the like.
Is the wall thermostat on a wall that is hot on the other side?

The highest setting on the Stat is +80 F. Stat is on an interior wall, away from the exterior glass windows. If the Stat is improperly installed (wired) would that cause a problem? I am at a loss as this is the second Stat I have had installed and both do the same thing, as if the temp sensor is not responding accurately (but two bad Stats, I think not). Also when heating, I can place my hand on the baseboard unit and though warm it s not hot, might the installer have mis-connect the wiring so I am only getting 125 versus 240, I need to get him back with a Volt meter. Any suggestions greatly appreciated.

I think the involvement of two thermostats may be the basic issue. I won't say that either is inaccurate, but may be that the temperature maintained by one is affecting the other to function. Not quite sure about this one.

"might the installer have mis-connect the wiring so I am only getting 125 versus 240,"
You are missing the concept. You say that the thermostat shuts off at 68 deg. That is not related to supply voltage. A 240 volt heater supplied at 120 volts will heat at 25% of the rated wattage. But no matter the voltage, you are not satisfied with the thermostat shutting off at 68 deg. 120 or 240 will not change that.
Where and how are you measuring the temperature?

I do not have two Stats installed, just replaced one and the second one gives same result.