Its clearly not-recommended by the rim manufacturer.
On top of that, the tyre has come off for you proves that its a bad combination.
That it is only 2mm is immaterial - it came off and could have severe consequences.
There is no glue or strap or ziptie or bodge-fix that will allow you to use this tyre and rim combination safely.
Your options are to buy a wider tyre, or replace the rim with something narrower. A 32 or 34mm tyre would be cheaper than a new rim, presuming the rest of your frame provides clearance for a wider tyre.
If your front rim is the same inner width, the same advice applies. If your front rim is narrower, then it might work with this tyre.