cell array dimensions do not match

I am having a problem where I am trying to create a cell array of strings to use in rmfield. I am combining a stem(chart) with a number (any number) to create the field I want to remove. For example, if I need to remove DeltaT.chart1, deltaT.chart6, deltaT.chart7, then my cell array would be:
chart1
chart6
chart7

The problem I have is when I get to chart 10 or more. If I have a number greater than 10 I would have the following:
chart1
chart6
chart7
chart10
and I get the error
??? Error using ==> vertcat
CAT arguments dimensions are not consistent.

Error in ==> remover at 28
            toremove = [toremove;field]

I think because I am trying to fit a 7 character wide (chart10) string into a 6 character wide cell array.

Is there a way around this or something I can do instead? My code is below if it helps.

Thanks,
Alex




for a = 17%1:22
    listremove = []
    toremove = []
    rmvr = 0;
    Fileone = 'NODIPSinBTBTB_Delta';
    File = [Fileone,'Comp',int2str(a)]
    
    load([Fileone,int2str(a),'.mat'])
    
    data = deltaT;
    stem = 'chart';
    
    for L = 1:length(fieldnames(data))
        field = [stem,int2str(L)];
        
        if length(data.(field)) == 0
            rmvr = 1
            listremove = [listremove L];
        end
    end
    if rmvr == 1
        for g = 1:length(listremove)
            field = [stem,int2str(listremove(g))]
            toremove = [toremove;field]
        end
        deltaT = rmfield(data, toremove)
    end
    
    save(File, 'deltaT')
    
    clear all

end