Is running a good form of exercise?

We currently have two months before our prom, and I would really love to tone up just a little before then. Lately, about every night, I have been running again (I was on the Cross Country Team at school back in the fall) and afterwards I usually try to do sit-ups and push-ups (so far I'm up to 30 sit-ups and then 30 push-ups, but I increase by 5 every night) and I also just recently bought two 8 Ib. weights, and I do 30 arm bend thingys with those (sorry I'm not sure what the proper term for that is) and thats bascially my exercise routine for the past week. However, I just don't feel like I'm getting anywhere, (even though I know it takes time) and I'm just worried what I'm doing isn't right, like theres better forms of excercise I should be doing in order to tone up my arms, legs, and stomach. Any one with any type of physical fitness experience or advice would be really helpful. I just want to know if what I'm doing is going to pay off in two months, or if I should switch up my excercise routine??? I'm also currently on a diet, but I just started two days ago, so I'm trying to watch what I eat as well. Any advice would be great though guys!! I'm wondering if all this excercise and dieting will make a difference by the time prom gets here too...I know it's healthier for me, but I'm scared I'll still look the same as I am now. I weigh 126 Ib. and I'm 5"3, so losing another 10 to 12 Ib. would be WoNdErFuL, but is it possible to do that in two month??? I'd love to look cute and skinny, because obviously I don't feel that way right now, and my arms look horrible, as well as my legs. I just feel fat compared to all the other girls at school, and I was pretty happy when like two months ago I had finally managed to get down to a size 4 in jeans, but now I feel like I should be even smaller, like a size 2 or 3!! Sorry I know I just bombarded this page with so many different questions, and A LOT of random, useless information, but I'm just very eager to find out whether what I'm doing now will work or not. Thanks for any help guys, I really appreciate it!!