dropping to one nap dilemma

My 13 month old has been working on dropping to one nap ... today was her first really successful day (learning curve) but now I am worried she's not getting enough sleep. She sleeps from about 7 or 7:30pm - 6:30 or 7am but she only naps an hour and a half. Today she woke up upset and nursed for about 10mins but did not go back to sleep. She is awake about 5 hours between sleeps and I cram her morning full of activity but I can't get her to nap longer.