Can I cable this relay to my regulator?
Your required load current is 3500W/230V = 15A. The normally-open (NO) contact is rated at 16A, so it is not exceeding the ratings. You don't need to (shouldn't) use the normally-closed (NC) contact, which is only rated at 8A. 

The coil current is minimal, and well within the 4A capability of your temperature controller (aka regulator). 

However, I strongly suggest you look at the life of this component. You are operating right at the maximum current, so you can expect it to last no longer than the 70,000 rated operations. At a 20 second cycle time it will wear out in a couple of weeks if operated 24/7 (continuously). Maybe that's acceptable for you, but it should be considered.