I developed a denovo assembler specially for chloroplasts and mitochondria. It can assemble a chloroplast in one contig within one hour from whole genome illumina data. I compared the results with MIRA and MITObim and it seems the quality is higher and it always assembles the whole chloroplast and only the chloroplast. As an output you get two fasta files, the only difference between them is the orientation of the region between the inverted repeats. If you blast both files against a reference you can select the correct orientation. I can send the link where you can download the tool, once it's online available.

Some chloroplast assemblies can be tricky because of an inverted and duplicated region. I'm not sure if this applies to your system, but I've heard complaints about it from botanists wading into HTS. Different assemblers will produce different results, so you might need to try a few and mess around with the settings a bit. Have you tried mapping your contigs back to a reference of some sort? Perhaps differential coverage is breaking up your assembly into multiple pieces and things are more-or-less okay; perhaps other things are going on.

The Milkweed Genome Project has a pipeline that passes arguments to several programs and might help out. Alternatively, I'd try using a reference-guided assembly if you can use a not-too-distant reference.

I also recommend ARC for breaking down the complex genome assembly problem into a more manageable one focusing on just reads that share similarity with the chloroplast. I've had great success with this for mammalian mitochondrial genomes, and others have used it for plastids.

You have a mix of plant, mitochondria and chloroplast contigs (and possibly other stuff), you need to sort them out. You may use blobology or simply blast to assign the contigs to genome, mitochondria and plastid. After you do that, follow the suggestions of brice.sarver to evaluate and/or improve you assemblies.

However, it is highly unlikely you will be able to assemble the whole chloroplast, due to the inverted repeats. You may get a small number of contigs covering most of it, though.