the deadline for making a 2018 contribution is the due date not including extensions for the tax return. thus you had until 4/15/2019 to make a 2018 contribution. you can even file your return before making the contribution and take a deduction.
if you contributed before 4/15/2019 what year did you tell the trustee the contribution was for? if 2018 you'll have to check with the trustee to see if it can be changed to 2019. if not, you;ll need to amend 2018 because you can't take a deduction for it in 2019. if after 4/15/2019 you're safe unless you designated it was for 2018, then the Trustee should have returned the contribution. if no year specified you have a 2019 contribution subject to whatever the rules are for IRA contributions that year
Is this a traditional IRA contribution or a Roth IRA contribution?
All traditional IRA contributions must be reported on the tax return for the year for which the contribution was designated.
A Roth IRA contribution is only required to be reported if it is an excess contribution since an excess contribution is subject to penalty. If the Roth IRA contribution qualifies you for a Retirement Savings Contributions Credit, it will be beneficial to report it and must then be reported on the tax return for the year for which the contribution was designated.
The year for which a traditional or Roth IRA contribution is designated is indicated by the year of the Form 5498 that shows the contribution. Form 5498 is prepared by the IRA custodian and sent to you and to the IRS.