The speaker is stuck in a loop of questions. Nearly every line asks something, and none gets answered. Someone has lied, and now they're wondering whether to confess, whether they should have been honest from the beginning, and whether anyone would believe them if they tried. The title plays on this: "Should I Should" sounds like a mind going round in circles, unable to move.
The feelings here are guilt, fear and self-doubt. In the first stanza the speaker looks backward with regret. In the second they look ahead, nervous about speaking "out loud" in front of "the crowd." The last stanza is the most revealing. The speaker admits they've put on a front of being strong, and they know the act was wrong. What worries them most is how they'll be seen, not only what they did.
The mood is anxious and unresolved. The simple, repeated question form makes it feel like a private, restless thought spiral, and the poem ends without any decision at all.