As a general rule, cooked and/or pureed fruit is allowed into the US, however you WILL need to declare it. Failing to declare it, even if it is otherwise allowed, can carry a fine and given the quantity you're going to be carrying being caught is certainly a possibility.
The quantity will not be relevant, unless customs believes that you are bringing in a "commercial" quantity. ie, more than would generally be considered for personal use. I would not expect 3kg to be considered a commercial quantity.
As is always the case, the final judgement is with the customs officials. Even if a product is allowed, they have the authority to seize it if they detect anything amiss. For example, even if a particular type of fruit was allowed, if there was evidence of that fruit containing bugs of some form then they would likely not allowed it in. (Obviously that's not not so much relevant for a marmalade, but the concept remains the same)
Full details on the rules can be found in the USDA's Miscellaneous and Processed Products Import Manual. Table 3-134 contains the details for "cooked fruit", whilst Table 3-151 specifically states that Marmalade is specifically allowed as long as it is properly packaged.
Marmalade IS considered a liquid/gel, which means standard international "liquid" rules would apply, meaning you could not carry more than 100mL per container in a carry-on bag, thus it would need to be in a checked bag.