Tamar Braxton Apologizes for Going Off After Trina's Engagement

Tamar Braxton is falling back into mea culpa mode just days after putting her sister, Trina, on blast for daring to get engaged ... during Tamar's birthday celebration.

ICYMI ... Tamar went off Tuesday on Trina's fiance, Von, after he popped the question to Trina. Tamar's issue is his timing sucked. The proposal went down on what Tamar considered a continuation of her bday bash. Check out the vid, Tamar rants about crappy gifts and Trina stealing her shine.

Tamar's now saying, "Oops!" She took to Instagram and said, "Sometimes you get so caught up in 'ME' you f*** up not only your night, but others as well! Looking at the bigger picture, I'm so excited and happy for [Trina] and [Von.]"

She didn't paint such a rosy picture earlier this week. Sources close to the situation tell TMZ ... Tamar's blowup was completely unwarranted because, for starters, the family celebrated Tamar's birthday on Monday.

We're told they had a birthday cake with candles and sang "Happy Birthday" ... the whole 9 yards. The next day -- when Tamar went off -- the family once again had dinner together to discuss their show, "Braxton Family Values."

The family meeting was NOT supposed to be another birthday bash ... especially since Tamar's birthday was March 17. Our sources say because the family got together again, Von felt it was a good time to propose ... especially because it's rare to get everyone together in the same room.

Our sources say Trina and Von do NOT feel like they stole Tamar's thunder -- after all, she'd already had her party.

We're told it's all water under the bridge now. As for Trina and the ring ... it's a beaut -- the center stone's nearly 2 carats.

It's a deep oval cut featuring another carat of smaller diamonds on the band. Congrats!!!