Lots of good advice here. Not to disagree with the sage advice, but... on the other hand, it's only two stops, right! It's not a disaster. My guess is that the negs will still print quite well if overdeveloped a tad. You could simply do a clip test (if your first or last frame wasn't important) and determine that you need a wee bit more development.
The thing about mistakes is that you can learn a lot from them! Once, I shot some IR film but... forgot to put on the IR filter!!! So the frames were all exposed by 8+ stops! The film developed to what look like pure black :roll: But, holding them up to bright light, I thought I saw a bit of detail. So I slapped them on a scanner and... surprise surprise, plenty of detail there. And the grain kinda worked with the scene.
If you do scan underexposed/underdeveloped b&w negs, you'll probably be amazed at what you can get, but it will be grainy and any dust or scratches will be prominent. Bathing the neg in selenium can help a little (not much, just a little, but enough to see in the result from the scanner).