Haha. Dont worry if she's a coworker. You're already showing signs that you're gonna f.uck this up so coworker or not, you're gonna blow it.
1. Having the first date on a weekend is the biggest no-no. You're a fun busy guy so you must have better things to do on a weekend... or is she the best thing you've got going on in your life right now?
2. You said "its getting harder not to go for it", that means she's really getting to you. I smell a oneitits coming.
3. "You don't feel pressured to talk to her like most other girls". Thats how it starts, right now her interest level is probably high, and yours is starting to grow. Pretty soon your interest will be so big that it will make her lose hers.
PS. NEVER feel pressure to talk to a girl. Do it because you feel like having fun. You never feel pressured to have fun right?
4. You say you already feel like an AFC. At least you recognize it, enough said.