I can't see that there's anything preventing a good experience on both your parts with what you've got. What you've got should do very nicely.
If you are still insecure, remember this, intercourse, especially for inexperienced women, can be an intimidating act. A bigger, stronger person is going to insert a part of his body into hers and thrust with it, at times, perhaps quite forcefully, until he climaxes. From that point of view, a penis can seem a lot larger than it really is. An average penis can be a real advantage. It is big enough to be an attractive organ, but not so big that she is genuinely afraid of it, but still big enough to be a tad intimidating for the woman (and thus a nice psychological booster for the guy).
For the most part, size is more a matter of psychology than physiology, especially amongst us guys. Each of us wants to prove to each other and our sexual partners who the "real man" is, but in reality nearly all of us are physically capable of getting the job done.
As for head, trust me, you are more than a mouthful, and that's all that matters.