Sex doesn’t feel good?

Hi. Last night, I (19M) did it for the first time with my girlfriend (19F). We were both virgins and didn’t really know how to do stuff but after using pornography as an example we gave it a shot. Turns out sex is a lot more physically demanding than what both of us imagined. When I entered her, it felt weird. Not in a bad way but also not in a good way. It was like my body was confused and don’t know how to process it? I always imagined it to feel like heaven from the way some people describe it. But that didn’t happen. The positions we did were doggy and missionary, everything else seemed too complicated. Even thought I didn’t really feel anything, I was still able to finish and my girlfriend said she enjoyed it. But I’m wondering if there’s something wrong with me or if this is just how sex is? No real feeling but it’ll make you pop?