Running less dna would give a more accurate assessment of size and show if there are 1 or 2 peaks in the strong band. Some possibilities are 1

The ladder is AT rich but the amplimer is GC rich and conformational differences make a size difference.

If the Amplimer is GC rich and you amplified in presence of 1M betaine then the salt in the sample may make it run slowly and look bigger.

The amplimer has SNPs in it and the single band is being split into 2 or more heteroduplexex which have a mismatch bubble in it so make the sample run slowly.

As you say sequencing will sort out what is happening.

I would highly recommend going for Gel extraction followed by sequencing to verify the distinct band just to make sure you are not amplifying the human genome.

Moreover, your bands look so thick and it's bleeding, I would say you can dilute the sample at least 1: 10 dilutions and repeat your experiment.

The observation of PCR bands larger than the expected size can be attributed to several factors. Here are some possibilities to consider:

Performing sequencing of the PCR products will provide valuable information about the identity of the unexpected bands and help elucidate the underlying cause of the observed amplification pattern. Additionally, troubleshooting steps such as optimizing PCR conditions and primer design parameters can help minimize nonspecific amplification and improve the specificity of the assay.

It may be due to genomic DNA contamination or the concentration is not appropriate, you can dilute your sample, repeat the experiment, and check. If still you face difficulties, I recommend you to go for sequencing to find out the exact problem

Primers might bind to undesirable sequences of template DNA sometimes, which led to amplification of the fragments larger than the target sequence.