Home pH kits can produce some highly inaccurate results and not all relatively new gardeners (or even more experienced ones) understand how to use them correctly. While I don't dispute your soil conditions may be acidic or even highly so, I think you need to investigate further.

FWIW, an accumulation of many years of leaves is very unlikely to produce highly acidic conditions. Soil acidity is the result of mineral deposits in the soil combined with high rainfall. Even very acidic types of organic matter (like oak leaves or conifer needles) are neutralized as they decompose and will not sway soil pH to any significant degree.

If you have brought in new soil and sand, then I would retest with a professional lab. Often local extensions offices will provide this service for you. Follow their directions for obtaining correct soil samples. The results from this test will be far more accurate than anything you could generate from a home test kit and they will also provide specifics for amendments to correct or neutralize any deficiencies.

Personally, based on your description of your exisitng situation and what you have already done, I'd be skeptical that your soil conditions are not already pretty adequate for growing beautiful flowers :-) I'd say go for it!

If you take your question to the Soil compost and mulch forum, you'll get lots of good answers.

annebert, is there some reason professional gardeners would not be able to address issues dealing with soil quality and pH? Perhaps even more so than many of the avid amateurs with widely varying opinions that post on the Soils forum? Soil issues are a major focus of my consultation and design business.