Django - form action url not redirecting with GET parameters

In my web page I have 3 forms where none, one or all of the form inputs can appear as parameters in the url.

The forms return values for:

sorting items
choosing a metric for items
page number

I use sessions to save all of these parameters, which stops them being overwritten by each other, and then I join them into a url parameter string which is then passed into the templates context.

The problem is when using <form action="{% url watchlist %}{{url_parameter_string}}"> only the parameter from its corresponding form is returned in the url, and does not return all of the parameters stored inside url_parameter_string.

views.py - watchlist view

if "url_params" in request.session:
    for k, v in request.GET.items():
        request.session["url_params"][k] = v
else:
    request.session["url_params"] = {}

request.session.modified = True

url_param_string = "?" + "".join([f"{k}={v}&" 
for k, v in request.session["url_params"].items()])[:-1]

context["url_param_string"] = url_param_string

url_param_string:

?graph-metric=max_price&sort-field=total_quantity-asc&page=1&view=items

html

<form action="{% url view %}{{url_param_string}}" method="GET">
    <label for="graph-data-form">Graph Data</label>
    <select onchange="this.form.submit()" name="graph-metric">
        {% for graph_option in graph_options %}
            <option value="{{graph_option.value}}">{{graph_option.text}}</option>
        {% endfor %}
    </select>
</form>

when the form is submitted

url