Boy & girl cat introduction

I just moved into an apartment with a couple of friends and they have a girl cat- meanwhile I have a very sweet and friendly boy cat. We let them adjust for a couple of days giving them their own space- and having them get used to each others smell. But when we went to introduce them after they were both settled with the new scents my boy cat so desperately wanted to be her friend. But she just hid under the bed, and hissed and yowled/growled at him while he was laying there patiently waiting for her. I just really want them to both be friends and adjust- I feel like I did everything right with a slow introduction but my friend’s girl cat is not adjusting well she won’t even come out to use her litter box or eat or drink. It worries me and my roommates.