I got bite by a bug that made a painful palm size bruise on my leg sold I be worried?

Not if. You are otherwise well and the lesion looks like a bruise and is not black or nasty appearing. Also reassuring if it resolves or improves over the next 2-3 days. See your doctor for any concerns. All the best. .
Bite. Nleave it alone and gift will heal. If it is itchy use a little Benadryl (diphenhydramine) cream.