I think some here are confused what the sex educator is doing Dr.Skipper - I was under the impression, this person was there to answer any questions and give advice...opposed to actually having sex. Am I correct? No judgements from me plus I thought your therapist gave this recommendation.
Regarding the 1st time - I admire you taking this seriously and being completely ready, so you don't regret the 1st time. Its different for some, but its not that painful and its normal. If you've done other foreplay down there and used toys - I think you'll be ready to receive this partner. I don't think you need to stretch yourself at all - the beauty of the 1st time from a man's point of view is, its supposed to be snug.....wink, wink. You're also assertive enough to say, "don't do it this way or slow down." You should also do plenty of foreplay and use lubricants. You may be over thinking this slightly. I'm giving you the same advice, I would give my own daughter when she's old enough for this experience. Hurting a little is normal, but I suspect it won't hurt much at all and you'll enjoy all you've anticipated. Best of luck and I hope this turns out to be a great experience with respect and caring for each other.