If it's been less than 60 days since the distribution from the Roth IRA, as long and you have not done an indirect rollover of an IRA distribution in the 12 months preceding this distribution and will not do another indirect rollover of any other distribution made in the 12 months following this distribution, you can roll back into the Roth IRA the portion that was not necessary to be distributed.
We are assuming that the Roth IRA custodian handled this correctly and will be reporting this as a regular distribution, not a return of contribution before the due date of your 2018 tax return because you apparently made no contribution for 2018 that would be eligible for such a return of contribution. However, some IRA custodians (particularly banks) are somewhat clueless with regard to proper procedures and will sometimes make a "return of contribution" when no contribution for the year was actually made. That often results in needing to file a substitute Form 1099-R (Form 4852) to report the type of distribution that was actually made. (If it doesn't qualify as a return of contribution before the due date of the tax return, it's a regular distribution no matter what the Form 1099-R provided by the payer says.)
