I know this is easier said than done but I would try really hard not to overthink how you reacted.
You had a huge trauma last year and I am so sorry for you. It probably hightens all your feelings at what is already a very emotional time.
My husband wants a boy more right now (18 weeks) so a part of me is nervous of finding out the sex. However deep down I know that whatever we have he will love and care for once it is born and I am sure your DF will be the same.
You are in no way a bad person for feeling unsure about the sex. I'm sure you really will both be happy with a healthy baby.
I think the loss of your beautiful boy would make you anxious either way, OP. As Hippolyta20 said, try not to overthink your reaction - and wait till your 20 week scan to find out for real what you're having. DH and I were convinced DC1 was a girl - turned out at the 20 week scan he was a boy and I had a distinctly disappointed reaction. However, nearly 7 years later and I wouldnt change him (or his little brother) for the world. Its natural to feel disappointed when pre-conceived ideas turn out to be incorrect - but you really do get over it.