Some women are built... smaller than others. Back in my misspent youth, I had a few relationships with women that took time to break in (and I mean that in the most loving and respectful non-horse-like way). If I may suggest, you should start with oral. Going down on her could help her learn to relax her vaginal muscles a bit. Once you've had a few of those, maybe start working in your finger, which is hopefully much smaller than your member. Work your way up to two, then three. Eventually, with a little help from Mr. lube, you should be able to get in there without her crushing you like the Mariana Trench.
Regarding your doubt leading to softness, you shouldn't think about it that way. It may be a penis defense mechanism. If I were about to make the loving with a woman that could snap my johnson off inside her, I suspect performance anxiety could kick in simply out of self-preservation. I like my penis unbroken.
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