You have to remove the new HTML block you tried to create. Can you login and navigate to the Home page? Once there do you have the “Change the blocks on this page” option? If you do then you should be able to remove the second HTML block from there.
If none of that is possible you will need to delete the block manually from the database. Your main / original html block I can see has an id number of 871, so:
1 – look in the table xx_block for a block with module_name = html and an id number other than 871. Just note its id for now.
2 – In the table xx_block_setting find that same id, and delete all it’s records. There will be at least three.
3 – Now return to xx_block and remove that html block from there as well.