We had same problem with dd2 in the early weeks. She's now 5 months, but at the beginning, she couldn't stay awake for as long as GF suggested, and she also wouldn't sleep for longer than 45 mins. Having had a model GF baby first time around, I was surprised. However, because the naptimes don't actually fit with the routine we need to have for our 3 year old (specifically the lunchtime sleep clashes with nursery collection!), I decided not to push things with the GF routine, and have gone with the flow a bit more.
I decided to follow Gina principles (majority food during the day, darkened rooms for naps, not too much sleep during the day), and not worry too much about what happened when.
In general, this has worked well, although I would have loved for her to sleep longer in the middle of the day. I am hoping that once she starts on solids, I may be able to encourage her to do this, because it's always seemed as though she's woken after 45 mins because she's hungry.
The main problem I have is that she does get very tired towards the end of the day, and, if I'm not careful, I either have an overtired baby who doesn't settle, or, if she's had a nap late in the afternoon, one who's had too much sleep and not enough food before bedtime.
I do think teething is playing its part (she has 2 teeth already). She's not on solids yet as I have been trying to stretch things out to 6 months, so there has been some confusion as to whether her recent increased night wakings are teeth or hunger. What I have tried is a bit of Calgel first, rather than instantly feeding her. If she settles back down easily then I know it's not hunger. I am lucky though, in that we've never had a problem with her settling herself (thumb).
HTh