As Marcia said, it's hard to say whether she's not a cuddler or if she still needs time without knowing how long she's been with you. It might just be that she needs time to adjust and get to know you better. The fact that she lets you pet her doesn't necessarily mean that she trusts you - at least not completely. Especially if she's shy, you'll need to let her come to you when she's ready. If you try to force it, she might become wary of you, and it will take longer.
My Celia is a total lapcat, but I don't believe she was like that for quite some time - maybe months? Maybe even longer (it's been 11 years, and I have a bad memory). It wouldn't have struck me as odd, because my other cat has never been a cuddler. Even now, though, Celia only asks for my lap when I sit down on the couch and turn on the TV. She knows that's the time when I'm relaxed and everything's calm and quiet. She's skittish and won't come out when I have guests and there's activity. Once we're all seated, chatting, and not moving, she comes out and sniffs everyone.
However, if you think that she's just not the right fit, maybe for other reasons that go along with her not being a cuddler, then this might not work out. This is still a trial run, right?