It's hard to be wise after the fact, but there's two golden rules to follow with important data.
Firstly, never burn irreplaceable data to just one disc. At minimum you should make two copies. Ideally make more than two copies - preferably using different disc batches (or even different disc manufacturers) for some of the copies. If you've got multiple drives that will write that type of media (such as a CD-RW and a DVD writer), use different drives for some copies if you can.
Secondly, always check that important discs are readable after you've written them - ideally in at least one different drive to those you wrote them in, and possibly on another computer entirely.
For now, probably your best bet is to download and try Isobuster.