Point 1: You knew the SOP was to to stay out of the heli space. With no permission otherwise ("never assume - check"), you were asking for a raspberry even if no helicopter had got in your way. I cannot work out what blind R/T calls you would be making once you had got yourself so far out of place. Airfield apportionments are for a very good reason. My experience includes a field with powered and glider users which in its past had a nasty history of fatal tangles. Such dissimilar flying demands studious care from all involved.
Point 2. I am not surprised the radio burst into life - you must have frightened the life out of the heli crew. If you wanted to frighten them you could not have pulled a better manoeuvre. I discovered this in basic military flying training. Airborne solo one sunny day I sighted a fellow course member before he saw me and chased after him. I passed under him undetected from behind, as conscious of his long undercarriage (peculiar to our Piston Provosts) as of my quite tall fin. Thanks no doubt to the endless ground school we had both endured, I put my faith in the concept of momentum. I counted three from when I heard his prop passing just overhead and effectively pulled into a half-loop. It was disappointing when I picked him up again to see him still straight and level. Of course when we landed I received all the reaction I might have hoped for - he remained livid with me for about a fortnight