now that you've already pushed to GitLab, aw.... :(

just to let you know, you could have done a rebase of 28b1dd4 and 231fae7 using:

git rebase --onto main mrbranch~2 mrbranch
git rebase --onto main 6a10acd 231fae7
# Your will be checked out at `main' after you run this.
# So you can `git push', `git push origin HEAD', or
# `git push origin HEAD:main', `git push origin main:main',
# `git push origin +refs/heads/main:refs/heads/main', etc.
# (Depends on how you feel I guess.)

(of course, don't run it now---you have already merged main, so...)

that way your history will be linear and... just nicer, in my opinion.
(a merge isn't really that bad though, git log ignores the commit graph
and lists commits in reverse chronological order anyways).
that said, since you ran `cs300 submit' and thus by then it already
pushed the submission to GitLab, you can't do much better than:

       NEW#2 <-+ PUSH
         |     :                          MERGE   <----+ PUSH
       NEW#1   :                       /         \     :
         |     :           OR          |         |     :
      SUBMIT (main)                    |      SUBMIT (main)
         |                (mrbranch) NEW#2       |
       OLD#2                           |       OLD#2
         |                           NEW#1       |
       OLD#1                           |       OLD#1
         |                             \         /
     (restart)                          (restart)

    new history                        new history
   based on main                     merged with main
  (my suggestion)                  (your current state)

because the main branch is **protected** on GitLab and so,
any update you make to it can only include more commits, not less.
And since GitLab already *has* your submission commit, it will
*always* contain that submission no matter what you do.
If you want to be able to remove your old commits, push to
something that *isn't* protected.  For example, I would do
`git push origin HEAD:devel' (devel can be any branch name
you like *except* main) and open GitLab to see if I am
satisfied with my commits.  If I am not, I can restart,
repeat the same thing (like what you did with your `mrbranch'),
then i can `git push --force origin HEAD:devel' which
essentially deletes my old commits (well, almost---we are
not given the control of the GitLab garbage collector.
but good enough for me. :)  Once I am happy, I can *then*
decide to push to the main branch by swapping that `devel' out
and putting `main` in there instead.
(Of course, I would remember clean up after myself using
`git push origin :devel'.)

according to @711 though, they will only grade the most recent
commits; so you should be fine (but well, of course, if it
weren't fine, it's not like there is anything you can do to
delete the old commits...)

=END=

P.S. not a part of the answer, but i personally think grading
based on a git repository is kind of a joke.