It is just a straight check
Spell Scroll (DMG 200)
If the spell is on your class's spell list but of a higher level than
you can normally cast, you must make an ability check using your
spellcasting ability to determine whether you cast it successfully.
The DC equals 10 + the spell's level. On a failed check, the spell
disappears from the scroll with no other effect.
Ability Checks (PHB 174)
To make an ability check, roll a d20 and add the relevant ability
modifier. As with other d20 rolls, apply bonuses and penalties, and
compare the total to the DC.
No bonuses or penalties are described in the Spell Scroll description, so you just add the modifier and nothing else.