It is actually quite common in many of the more advanced pieces to require the thumb to play two notes at the same time. Don't worry about it.
Most correct - and, many scores put brackets around those two fingers to show you that it is not only okay, it is recommended. Further, there are some single notes (black keys) where if I have to reach for a black key in my right hand, I strike the note with my third finger, with my fourth finger welded to it.
Finally, if in doubt, per my video, most pianists in the 19th century would have rolled the chord. In one particular section of the Brahms Intermezzo Op. 118 No.2, I actually take two notes with the thumb and roll the rest of the chord.
The point, as stated numerous times in Earl Wild's Memoir, pianists, of the 19th and early 20th centuries, regularly re-arranged certain chords to better fit their particular hand. And, no one said anything about it!
Enjoy my video.