You performed a conversion. You rolled over your pretax 401k funds into a Roth IRA, which becomes a Roth conversion. The bad news is that it is fully taxable now, and can't be reversed or recharacterized. (You can't undo it and put the money in a regular IRA, for example.)
The good news is that once you pay the tax now, and as long as you leave the conversion funds in the Roth IRA for at least 5 years, that money will never be taxed again. You also won't have to take RMDs in retirement.
