I'm really small and a bit chubby so lately I've been working out. I've gained weight and now a look littler but quite muscly like a runner with big legs. I just want to get slimmer?

Its not fat, its muscle. I'm like that and I run track so it's good that you have runners legs. The scale might say you gained weight because muscle weighs more than fat. So don't weigh yourself. Just look in the mirror and decide if you look good or not.