You are bottling way too early -- it's very likely that you have dissolved CO2 in the wine, plus it's unlikely the wine is clear. Are you getting sediment in the bottle?
What kind of bottles are you using? Unless the bottle is designed for pressure (beer or champagne bottles), it's potentially dangerous to do anything that produces pressure. If the bottles are corked, you'll produce mini-volcanoes and get to clean up mess. If the bottles are screwcap, you are potentially producing grenades if the pressure exceeds the glass's capacity. Bottles not produced explicitly to handle pressure (beer and champagne bottles) are not rated to handle ANY pressure, and can explode.
I suggest unbottling the wine and putting it in carboy(s) under airlock to let it complete fermentation and to clear. Give it 3 months, and you'll see tremendous difference.
If you want to make a sparkling wine (sparkling mango sounds cool!) add 1/2 to 3/4 cup sugar to 5 US gallons / 19 liters of wine, and stir very well. Bottle in beer or champagne bottles, and crown cap. Put the bottles someplace warm (70-85 F) for a few weeks, then age at least 3 months (a year is better, but we all know you're going to open one before then.
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Regarding bitterness, CO2 can cause that. It's true that most fruit wines benefit from backsweetening, even a bit. This eliminates astringency and enhances fruit flavors. Before backsweetening, add potassium sorbate and potassium metabisulfite (K-meta) to a clear wine. This prevents the yeast from eating the new sugar, which produces CO2 and brings us back to NOT making grenades or mini-volcanoes ...
