I haven't read the other replies so hopefully I'm not repeating anything.
First, relax. Going back to work is stressful and hard. But your baby's gonna pick up on your stress too. I think most bf babies would rather have mom than a bottle. But if mom's not there, that bottle might not look too bad. My youngest wouldn't take a bottle if I was even in the house. Without me around, he'd take a bottle, though it never was his favorite thing.
My first day back to work after I had him (he was 6 weeks old), was rough. But we both got used to it and it ended up being ok. He did reverse cycle, which worked out fine for me since I couldn't pump much anyways. And he got to where he'd take a bottle or two a day. He did eventually start sleeping all night and drinking all his bottles during the day as he got older.
If you can go nurse on your lunch break, that will probably help ease you both into this. Good luck, you can do this and you'll both be fine!