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Firstly have you checked that your rooms are meeting their temperatures requirements, if not, I would make sure that your zone sizing and system sizing objects are showing the correct values for sizing the radiant slabs. Secondly, if your rooms are meeting setpoint there are a few things you might want to check with a quick hand calculation:

1. envelope properties, is you envelop well insulated? if so the heating demand from the space is going to be lower than if there is very little insulation
2. infiltration rates, do you have a lot of outside air coming into your space through infiltation, if so your heating demand will be higher than with a tight envelop
3. lighting and plug load in the spaces, 4W/ft² seems quite a large load to me for a residential space, i would expect something closer to 2W/ft². You might want to check these and then check the schedules you have applied to them, are the lights and equipment on 24 hours a day, is this realistic
4. how are you putting fresh air into the space (through the DOAS?) what temperature is this air entering the space and what is the flow rate, the higher the flow rate and temperature the less work the radiant slabs have to do.

My suggestion is to take all these numbers and for the heating design day (and/or for the average temperature each month) calculate what your heating demand is. Check this against the simulation and make sure all your inputs are what you would expect. Then if things still aren't working as expected, I would suggest reading the inputoutput guide, this will help you understand the objects you are using better.