git newbie in here.

I had 2 branches a and b in my local repo. 
so if i do 

```
git branch
*a
b

```

then by mistake i did "git pull origin" and it pulled a bunch of files and messed my working environment on branch a.

I wanted to revert back. I wanted to undo "git pull origin" - how can i do that??

I tried "git pull origin a" but then it gives me hundreds of files to be merged and it gives the following message after a big list of files:

Pull is not possible because you have unmerged files.
Please, fix them up in the work tree, and then use 'git add/rm '
as appropriate to mark resolution, or use 'git commit -a'.

I tried "git reset --hard" but this doesn't bring the files that I wanted to work on. What can i do to fix this??

One piece of info that might help: before doing "git pull origin" the response to "git log" was commits of my team only (which was working on that branch only) but now after i did "git pull origin" the result of "git log" is status from everyone in the company.

Please help me. Thanks